Umar ibn Abd al-Aziz: The Reforming Caliph

Umar ibn Abd al-Aziz, the eighth caliph of the Umayyad dynasty, ruled from 99 to 101 AH (717–720 CE) — a reign of roughly two and a half years, one of the shortest of the dynasty and by common assessment the most consequential in its effect on how the caliphate was understood. He is the one Umayyad ruler whom the later Sunni tradition, largely hostile to the dynasty, treats as an exemplary figure, and he is often described in that literature as a mujaddid, a renewer of the faith.

His reign is significant less for what it accomplished durably — most of his measures were reversed within a few years of his death — than for what it attempted. He acted on the premise that the caliphate was a trust accountable to religious law rather than a patrimony of his family, and he applied that premise to taxation, to landholding, to the treatment of non-Arab converts, to the conduct of war, and to the household of the dynasty itself.

Descent and Upbringing

Umar was the son of Abd al-Aziz ibn Marwan, a son of the caliph Marwan I and long-serving governor of Egypt, and therefore a nephew of the caliph Abd al-Malik and a cousin of the caliphs who ruled during his lifetime. His mother, Umm Asim Layla, was a granddaughter of Umar ibn al-Khattab, the second of the Rightly Guided Caliphs. He was thus a great-grandson of Umar I on his mother's side, and he was given that ancestor's name.

The sources place his birth around 61 to 63 AH, corresponding to roughly 680 to 683 CE, and the exact year is not settled; his birthplace is usually given as Medina, though some accounts associate his early years with Egypt, where his father governed. The variation reflects the state of the record rather than a substantive dispute.

What is consistently reported is the character of his education. He was raised and schooled in Medina, the city where the scholarly tradition of the Hijaz was taking shape, and he studied with its jurists and traditionists. This formation distinguished him sharply from the Umayyad princes brought up in the Syrian court, and it supplied both the intellectual framework of his later policy and his personal network among the scholars. The circle of Medinan learning that shaped him was the same environment that, a generation later, would produce Malik ibn Anas.

Governor of Medina

In 87 AH (706 CE) the caliph al-Walid ibn Abd al-Malik appointed Umar governor of Medina, and his authority was subsequently extended over the wider Hijaz including Mecca. He was in his mid-twenties.

His conduct in the post prefigured his caliphate. Rather than governing through the customary apparatus of appointed officials alone, he constituted a consultative body of Medinan jurists — the sources generally speak of ten — and undertook to decide matters in consultation with them. He also carried out repairs and extension work on the Prophet's Mosque during his tenure.

His governorship ended in 93 AH (712 CE) after friction with al-Hajjaj ibn Yusuf, the powerful governor of Iraq. Medina had become a refuge for people fleeing al-Hajjaj's administration, and Umar declined to return them. Al-Hajjaj pressed the caliph, and Umar was removed. The episode established his reputation for resisting the coercive style of provincial government that characterised the period, and it cost him office.

Accession

The manner of Umar's accession was unusual. The caliph Sulayman ibn Abd al-Malik, on his deathbed in 99 AH (717 CE), designated Umar — a cousin — as his successor, passing over his own sons and brothers. The accounts attribute a role in this arrangement to Raja ibn Haywa, a respected figure at the Syrian court, and describe the designation as being kept sealed until Sulayman's death so that it could not be contested in advance.

The sources also record Umar's own reluctance. Reports describe him addressing the assembled Muslims and offering to release them from allegiance if they wished to choose another, and expressing dismay rather than satisfaction at the office. The biographical literature treats these accounts as characteristic; they are reported traditions about his disposition rather than independently documented events.

The Reforms

Umar's programme was wide-ranging and pursued with unusual speed.

The status of non-Arab converts

The most structurally important of his measures concerned the mawali, the non-Arab converts to Islam. Under the fiscal system as it had developed, conversion did not reliably relieve a subject of the tax burden attached to non-Muslim status, and in several provinces converts continued to pay the poll tax. This produced a grievance of the first order: it implied that the empire's revenue depended on its subjects not becoming Muslim, and it made conversion economically punitive.

Umar ruled that a convert to Islam was not liable to the poll tax. He instructed his governors accordingly, and the reports describe his rejecting the fiscal objection outright — the position attributed to him being that God had sent the Prophet as a caller to faith and not as a tax collector. The measure struck at the revenue base of provinces such as Egypt and Khurasan, and provincial administrators resisted it.

He also addressed the related question of kharaj land, the tax-bearing agricultural land of the conquered provinces, restricting its alienation into private Arab estates so that the land tax could not be evaded by transfer of title. The problem he identified here — the tension between an Arab landholding elite and a fiscal system premised on conquered land remaining in the hands of its cultivators — outlasted him and remained a central difficulty of Umayyad and early Abbasid government.

Restitution and the dynasty's wealth

Umar established a process for hearing claims of wrongful seizure — mazalim, grievances — and for returning property taken by members of the ruling family. The sources report that he began with his own holdings and those of his immediate relatives, and that he divested himself of estates and revenues that had come to him by virtue of his position. He curtailed the stipends and privileges of the Umayyad house, and the resentment this generated among his kinsmen is a recurring theme in the accounts of his reign and death.

The tradition also preserves reports of a treasury in surplus and of difficulty in finding eligible recipients for zakat in some districts. These reports come from a literature that regarded his reign as a model, and the more cautious modern assessment treats them as indicative of the direction of his fiscal policy rather than as statistical description.

War and the frontiers

Umar reversed the dynasty's posture of continuous expansion. The great Umayyad siege of Constantinople, mounted under his predecessor and commanded by Maslama ibn Abd al-Malik, was failing when he took office; he ordered the withdrawal of the army. He similarly declined to press campaigns on other frontiers and concentrated on consolidating and administering what the state already held.

The reasoning attributed to him combines the practical and the religious: the human and financial cost of the campaigns was not justified by their prospects, and the obligations of just government within the territory of Islam took precedence over its extension. The policy was abandoned by his successors.

Religious policy and the collection of hadith

Umar ended the practice, established under earlier Umayyad rule, of denouncing Ali ibn Abi Talib from the pulpits in the Friday sermon, substituting a Quranic verse in its place — the verse usually identified in the sources being Quran 16:90, on justice and kindness. The measure removed a standing public insult to the Prophet's family and is among the reasons his memory is treated with comparative respect in traditions otherwise critical of the dynasty.

Other acts of conciliation toward the Ahl al-Bayt are reported. Sources record him restoring to the descendants of Fatimah the estate of Fadak, the property in the Hijaz whose disposition after the Prophet's death had been contested from the outset. This report is preserved principally in Shia historical literature, and the underlying dispute over Fadak is a matter on which the traditions differ substantially; it is recorded here as reported, with that attribution, and the dispute itself is not adjudicated in this article. What the reports establish in aggregate is a deliberate change of posture: a caliph of the house that had fought Ali and killed his son at Karbala choosing to reduce rather than maintain the dynasty's antagonism toward the Prophet's family.

His most enduring initiative in the religious sphere was administrative. He instructed the authorities in Medina — the accounts name Abu Bakr ibn Muhammad ibn Amr ibn Hazm — to gather the hadith and the sunnah in written form, and the scholar Muhammad ibn Muslim ibn Shihab al-Zuhri is associated with the resulting effort. This is generally identified as the first official, state-sponsored attempt at systematic written collection of prophetic tradition, undertaken from the concern that the material was being lost as the generation that carried it died out. The compilations produced under this instruction have not survived independently, but the effort stands at the beginning of the process that led to the great collections of the third Islamic century.

He also engaged the Kharijite opposition by argument and correspondence rather than by immediate military suppression, sending representatives to debate them — an approach that distinguished his handling of dissent from that of his predecessors and successors alike.

Reports concerning his treatment of non-Muslim communities are mixed. Some accounts credit him with insisting on the protections owed to them under the dhimmi arrangements and with restraining official abuses; others attribute restrictive administrative measures to him. The material is uneven and shaped by the outlook of the transmitting sources, and no single characterisation can be firmly established from it.

Death

Umar died at Dayr Sim'an in Syria in Rajab 101 AH, corresponding to February 720 CE. He was about forty years old, and had ruled for roughly two years and five months. He was buried at Dayr Sim'an rather than in the dynastic burial places, and the sources record his instruction that his funeral be conducted without display.

A number of accounts state that he was poisoned by members of his own family who stood to lose from his reforms. The reports are early and widely repeated, and the motive they describe is consistent with the documented resentment his measures provoked; but the claim is not independently established, and the more cautious historical treatments record it as a persistent tradition rather than a demonstrated fact. He was succeeded by Yazid ibn Abd al-Malik — Yazid II — under whom the substance of the reform programme was set aside.

The State He Inherited

Understanding the reforms requires some sense of the condition of the caliphate in 99 AH, because Umar was not addressing abstract questions of justice but a specific and deteriorating set of arrangements.

The Umayyad state had been built by conquest and was still organised for it. Its revenue came overwhelmingly from the land taxes of the conquered provinces — Egypt, Syria, Iraq, and the Iranian lands — and from the poll tax on non-Muslim subjects. Its army was drawn largely from the Arab tribal levies settled in garrison cities, paid from provincial revenue, and expected to be employed. Its administration had been inherited wholesale from Byzantine and Sasanian practice, staffed in the provinces by the same families that had served the previous empires, and only partially translated into Arabic.

Three pressures had accumulated within this structure. The first was fiscal: the conquests had slowed, and with them the flow of plunder that had subsidised the system, while the standing obligations to the Arab military class continued. The second was the question of the mawali. Conversion to Islam was proceeding steadily in the provinces, particularly in Iraq and Khurasan, and each convert represented both a fiscal loss and a claim to the status and stipends of a Muslim. Provincial governors had responded by continuing to levy the poll tax on converts, which preserved the revenue and created a class of Muslims who were taxed as though they were not. The third was legitimacy. The dynasty had come to power through civil war, had ruled through the suppression of successive revolts, and had presided over the killing of the Prophet's grandson at Karbala. Among the pious circles of the Hijaz and Iraq, Umayyad rule was widely regarded as a departure from the pattern of the Rightly Guided Caliphs.

Umar's reforms addressed all three, and it is the coherence of the programme — fiscal, social, and religious at once — that distinguishes his reign from the piecemeal adjustments of his predecessors.

Method of Government

Umar governed largely by written instruction. The classical sources preserve a substantial body of letters and administrative orders attributed to him, addressed to governors, tax officials, and judges, and this correspondence is the closest thing the early caliphate offers to a statement of governing philosophy from a ruler's own hand. Its authenticity is not uniform — the corpus grew in transmission, and some items are clearly later — but the core is treated by historians as reflecting his administration.

Several themes recur in it. Governors are told that their authority is delegated and accountable, and that the treasury is held in trust rather than owned. Tax officials are instructed not to exceed the assessed demand, not to use coercion in collection, and not to levy on those exempt. Provincial officials are directed to hear grievances directly and without intermediaries. And there is repeated insistence that the cultivator must be left with the means to cultivate again the following season — a principle of fiscal self-interest as much as of charity, and one that recurs in later Islamic writing on statecraft.

He also changed who governed. Several of the more notorious provincial appointees of the previous reigns were dismissed, and men associated with the scholarly and pious circles were appointed in their place. This was a deliberate reversal of the dynasty's practice of ruling the provinces through hard men with a free hand, and it was among the changes most quickly undone after his death.

The removals mattered because of who they were. Umayyad provincial government in Iraq and the east had rested for decades on governors of the type of al-Hajjaj ibn Yusuf — administrators of proven capability who held turbulent provinces by force and whose methods the caliphs tolerated because they produced revenue and quiet. Yazid ibn Abi Muslim, al-Hajjaj's protégé, was removed from North Africa; the pattern was repeated elsewhere. The replacements were chosen for probity rather than for the ability to intimidate, and the accounts record that some of them proved less effective at collecting revenue, which was precisely the objection their opponents raised.

There is a structural observation to make here that the sources themselves imply. The Umayyad state had come to depend on a particular kind of governor, and dispensing with that kind required either accepting lower receipts or reforming the fiscal system so that receipts did not depend on coercion. Umar attempted the second, and the shortness of his reign meant the attempt was still incomplete when he died.

Abolished exactions

Beyond the poll tax on converts, Umar addressed a category of levies that had accumulated outside the canonical taxes of Islamic law. The sources describe him abolishing various customs charges, market dues, and irregular impositions collected by provincial officials — exactions with no basis in the recognised categories of zakat, kharaj and jizya, which had grown up because they were convenient and because nobody with authority had objected.

The reasoning attributed to him is legal rather than economic: taxation must rest on a warrant in the sources, and a levy without one is simply appropriation. The same principle underlay his handling of confiscated estates. Its practical effect was to reduce the revenue available to provincial administrations, which is among the reasons those administrations resisted him and among the reasons his successors reversed him.

The Kharijite Question

The Kharijites, who held that leadership belonged to the most qualified Muslim regardless of descent and that a sinful ruler forfeited authority, had been in intermittent armed revolt against both Ali and the Umayyads for decades. The standing Umayyad response was military suppression.

Umar's approach was different. The accounts describe him corresponding with Kharijite leaders and sending representatives to debate them, inviting them to state their grievance and undertaking to correct any wrong they could demonstrate. Reports indicate that his interlocutors found the argument difficult to sustain against a ruler whose conduct they could not readily condemn, and that fighting subsided in his reign. The engagement did not resolve the doctrinal dispute, and hostilities resumed under his successors; but it stands as an early instance of a caliph treating a theological opposition as a party to be answered rather than only a rebellion to be crushed.

The Reversal

The most striking fact about Umar's reforms is how little of the structure survived him. Yazid II, who succeeded in 101 AH, restored the fiscal practices Umar had abolished, reinstated dismissed officials, and returned to the dynasty's earlier pattern of provincial government. Under Hisham, who followed, expansion resumed on several frontiers.

The reasons are not obscure. The reforms cut directly into the material interests of two powerful constituencies — the Umayyad family and the Arab military and landholding elite of the provinces — and Umar had held office for barely thirty months, insufficient time to entrench a new arrangement or build a body of officials committed to it. His programme depended on the personal authority and moral standing of one man, and it did not outlast him.

What did outlast him was the demonstration. The grievances he identified continued to accumulate, and the coalition that overthrew the dynasty in 132 AH drew heavily on the non-Arab Muslims whose fiscal and social position he had tried to regularise. Later writers, assessing the fall of the Umayyads, treated his reign as the moment when the dynasty was shown what it might have done and declined to do.

Umar as a Scholar and Transmitter

Umar's standing in Islamic literature is not only that of a just ruler; he holds a place in the scholarly chain as well, and this is part of why the tradition treats him differently from his relatives.

He belonged to the generation of the tabi'un, the Followers — those who did not meet the Prophet but who studied with his Companions. His Medinan education placed him among the students of that generation's leading figures, and he is counted in the biographical literature as a transmitter of hadith in his own right. Material on his authority appears in the collections, and Malik ibn Anas transmits from him in the Muwatta. Al-Dhahabi's biographical notice treats him as a jurist as well as a caliph, and later writers cite legal opinions attributed to him.

This dual standing had a practical effect on his government. A ruler who could himself discuss a point of law with the scholars of Medina was in a different position from one who had to receive their judgement as an outside constraint, and the sources present his reforms as arguments from the sources rather than as acts of royal will. It also explains the ease with which the pious circles of the Hijaz and Iraq accepted him, having opposed his predecessors.

The advice literature that grew around him belongs to this context. A letter of counsel on the duties of a just ruler, addressed to him by the Basran preacher al-Hasan al-Basri, circulated widely and was quoted for centuries; it sets out the imam as the support of the weak and the redress of the wronged. Such texts are advice literature rather than documentary record — the tradition of counsel to rulers attracted attributions readily, and their transmission is not uniformly secure — but their existence indicates how quickly his reign became the reference case for the subject.

North Africa and the Berbers

One province illustrates Umar's approach with unusual clarity, and it is often passed over.

The Maghrib had been conquered in the decades before his accession, and the Berber populations of North Africa had converted to Islam in large numbers and supplied much of the manpower for the conquest of Iberia under Musa ibn Nusayr and Tariq ibn Ziyad. Their treatment afterwards did not reflect that contribution. Berber Muslims were classed as mawali — clients of the Arab tribes — received lower pay than Arab soldiers, and were largely excluded from the spoils of the conquests they had fought in. Beyond this, the Arab administration levied tribute in human beings on Berber tribes, supplying the ruling class with slaves.

Umar is the only Umayyad caliph known to have condemned that levy and ordered it discontinued. He also despatched a group of scholars — the sources speak of ten men of the tabi'un — to North Africa specifically to teach Islam to the Berbers, treating the province as a field for instruction rather than only for extraction.

The measures did not survive him, and the consequence was substantial. The conviction that Islam and Umayyad rule were separable things, and that the dynasty's practice contradicted the religion it invoked, took deep root in the Maghrib. Berber revolts against Umayyad authority began within two decades of Umar's death, and North Africa subsequently proved receptive to movements — Kharijite and others — that rejected the eastern caliphate altogether. Umar's brief correction is cited in the literature as evidence of what the dynasty had been told and had chosen not to do.

Household and Personal Conduct

The biographical tradition devotes considerable attention to Umar's domestic life, and while this material is devotional in tone it bears on the substance of his policy, since his programme of restitution began inside his own house.

He was married to Fatima bint Abd al-Malik, a daughter of one caliph and sister of others — a marriage that had bound him to the centre of the dynasty. The most frequently repeated report of his reign concerns her jewellery: on his accession he required her to choose between her jewels, which had come from the caliphal treasury, and remaining in his household, and she surrendered them to the public treasury. Whether the exchange occurred as narrated cannot be established, and the report clearly served an edifying purpose in the retelling; but the underlying claim — that he divested his own family of assets derived from the state — is consistent with the administrative record of his restitution policy.

The same literature describes an austerity in his personal expenditure that contemporaries found startling in a caliph: plain dress, a reduced household, the sale of luxuries acquired by his predecessors, and the refusal of state resources for private use. Reports also describe him declining to use official candles or lamps for personal correspondence.

These accounts should be read for what they are. They come from a tradition that had settled on him as its model of just rule and that shaped its material accordingly, and their specific details cannot be verified. Their historical value is that they are consistent with the documented policy, and that they record what the following generations thought a caliph ought to be — a standard constructed largely out of his reign.

Relations Beyond the Frontier

Umar's reversal of the expansionist posture extended to diplomacy, and the sources preserve traces of contact with the Byzantine empire during his caliphate.

His military decision was clear enough: the army before Constantinople was withdrawn, and forces were also pulled back from exposed positions in Cilicia, consolidating the defensive line closer to the Syrian heartland. This ended the most ambitious offensive the dynasty had mounted against Byzantium and marked the point at which the Umayyad state ceased to treat the conquest of the Byzantine capital as an achievable objective.

Alongside this, Islamic and Byzantine sources report an exchange of letters between Umar and the emperor Leo III on questions of religion. Texts purporting to be that correspondence survive in several versions and languages. Their authenticity is disputed: scholars have argued variously that they preserve a genuine exchange, that they are later compositions built around a real diplomatic contact, and that they are wholly literary. The correspondence is therefore noted here as a reported episode of contested authenticity rather than as established fact, and no argument in this article rests on it.

Assessment and Legacy

Umar ibn Abd al-Aziz occupies a singular position in Islamic historical memory. The Umayyad dynasty is treated critically in the mainstream of later Sunni historiography, which was largely composed under Abbasid patronage and which measured the Umayyads against the standard of the Rightly Guided Caliphs. Umar is the exception: the literature places him close to that standard, and it became common to describe him as a renewer of the religion at the turn of the first Islamic century, with some writers naming him a fifth rightly-guided caliph.

Four points can be stated with reasonable confidence.

His fiscal and conversion policy identified a genuine structural contradiction in the early Islamic empire — that a state built on the tax revenue of non-Muslim subjects had no coherent way to absorb their conversion — and it addressed that contradiction directly. The problem was not solved in his reign, and the pressure it generated contributed to the discontent among non-Arab Muslims that helped bring the Umayyads down a generation later.

His instruction to collect hadith in writing had consequences far beyond his reign. Whatever the fate of the specific compilations, the principle that the state had an interest in the systematic preservation of prophetic tradition was established, and the scholarly effort it set in motion fed directly into the formation of the discipline.

His treatment of the Berbers and of the mawali generally shows that the problem was understood at the time and was soluble in principle. That his successors reversed the correction, and that the Maghrib drew the conclusion that Islam and Umayyad rule were separable, is among the clearer causal threads running from his reign to the dynasty's fall.

And his reign supplied later Muslim political thought with a working example of a caliph who treated the office as accountable to law. Writers on governance across the following centuries returned to his administration for that reason, and the durability of his reputation — in a tradition otherwise unsympathetic to his family — rests on it.

A caution belongs with all of this. The sources on Umar are unusually laudatory, and the biography by Ibn Abd al-Hakam, the earliest dedicated treatment, is a work of admiration rather than of scrutiny. The administrative measures are corroborated across independent lines of transmission and by the fiscal histories, and can be treated as established; the anecdotes of personal piety cannot be verified individually and are best read as the tradition's portrait of the ideal ruler, drawn from his reign rather than photographed in it.

References and Further Reading

Primary Islamic Sources

• Quran, Surah al-Nahl (16:90) — "Indeed, God orders justice and good conduct"; the verse the sources report Umar substituting for the denunciation of Ali in the Friday sermon
• Quran, Surah al-Nisa (4:58) — on rendering trusts to their owners and judging with justice, a text central to the conception of office reflected in his administration
• Quran, Surah al-Hashr (59:7) — on the distribution of public wealth, cited in the discussions of his fiscal measures
• Sahih al-Bukhari and Sahih Muslim, Books of Leadership (Kitab al-Imarah) — the prophetic material on the responsibilities of rulers against which his reign was measured by later writers
• The corpus of letters and administrative instructions attributed to Umar, transmitted in the classical histories and biographical works

Classical Islamic Sources

• Ibn Abd al-Hakam. Sirat Umar ibn Abd al-Aziz. [Compiled 9th century CE] — the earliest dedicated biography, the principal classical source for his reign
• Ibn Sa'd, Muhammad. Al-Tabaqat al-Kubra. Edited by Eduard Sachau. Leiden: Brill, 1904–1940. [Compiled c. 845 CE] — extended notice on his upbringing, governorship, and death
• Al-Tabari, Muhammad ibn Jarir. Tarikh al-Rusul wa al-Muluk. Edited by M.J. de Goeje. Leiden: Brill, 1879–1901. [Completed c. 915 CE] — the narrative of his accession, reign, and the withdrawal from Constantinople
• Al-Baladhuri, Ahmad ibn Yahya. Futuh al-Buldan. Beirut: Dar al-Kutub al-Ilmiyyah, 1987. [Original c. 892 CE] — the fiscal and land-tax measures, and their provincial application
• Al-Dhahabi, Shams al-Din. Siyar A'lam al-Nubala'. Beirut: Mu'assasat al-Risalah, 1981–1988. [Compiled c. 1348 CE]
• Al-Suyuti, Jalal al-Din. Tarikh al-Khulafa. Cairo: Dar al-Fajr lil-Turath, 2004. [Compiled c. 1500 CE]

Academic and Scholarly Sources

• Kennedy, Hugh. The Prophet and the Age of the Caliphates. 3rd ed. London: Routledge, 2016.
• Hawting, G.R. The First Dynasty of Islam: The Umayyad Caliphate AD 661–750. 2nd ed. London: Routledge, 2000.
• Cobb, Paul M. "Umar b. Abd al-Aziz." In Encyclopaedia of Islam, 3rd ed. Leiden: Brill.
• Dennett, Daniel C. Conversion and the Poll Tax in Early Islam. Cambridge: Harvard University Press, 1950. — the standard study of the fiscal problem Umar attempted to resolve
• Crone, Patricia, and Martin Hinds. God's Caliph: Religious Authority in the First Centuries of Islam. Cambridge: Cambridge University Press, 1986.
• Judd, Steven C. Religious Scholars and the Umayyads: Piety-Minded Supporters of the Marwanid Caliphate. London: Routledge, 2014.
• Blankinship, Khalid Yahya. The End of the Jihad State: The Reign of Hisham ibn Abd al-Malik and the Collapse of the Umayyads. Albany: SUNY Press, 1994. — on the frontier policy Umar interrupted and his successors resumed

Further Reading

• Hallaq, Wael B. The Origins and Evolution of Islamic Law. Cambridge: Cambridge University Press, 2005.
• Siddiqi, Muhammad Zubayr. Hadith Literature: Its Origin, Development and Special Features. Cambridge: Islamic Texts Society, 1993. — on the early written collection of hadith and Umar's instruction
• Lapidus, Ira M. A History of Islamic Societies. 3rd ed. Cambridge: Cambridge University Press, 2014.
• Al-Mawardi, Ali ibn Muhammad. Al-Ahkam al-Sultaniyyah (The Ordinances of Government). Cairo: Dar al-Hadith, 2006. [Original c. 1058 CE] — the later theory of just rule to which his reign was a standing reference