Abū Jaʿfar Hārūn ibn Muḥammad al-Wathiq bi'Llah (; ( 200-232 AH | 812-847 CE), commonly known by his regnal name al-Wathiq bi'Llah (), was an Abbasid caliph who reigned from 842 until his death in 847.

Al-Wathiq is described in the sources as well-educated, intellectually curious, but also a poet, who enjoyed the company of poets and musicians as well as scholars. His brief reign was one of continuity with the policies of his father, al-Mu'tasim (), as power continued to rest in the hands of the same officials whom al-Mu'tasim had appointed. The chief events of the reign were the suppression of revolts: Bedouin rebellions occurred in Syria in 842, the Hejaz in 845, and the Yamama in 846, Armenia had to be pacified over several years, and above all, an abortive uprising took place in Baghdad itself in 846, under Ahmad ibn Nasr al-Khuza'i. The latter was linked to al-Wathiq's continued support for the doctrine of Mu'tazilism, and his reactivation of the to root out opponents. In foreign affairs, the perennial conflict with the Byzantine Empire continued, and the Abbasids even scored a significant victory at Mauropotamos, but after a prisoner exchange in 845, warfare ceased for several years.

Al-Wathiq's character is relatively obscure compared to other early Abbasid caliphs. He appears to have been a sedentary ruler occupied with the luxuries of the court, a capable poet, and a patron of poets and musicians, as well as showing interest in scholarly pursuits. Al-Wathiq's unexpected death left the succession unsettled. Al-Wathiq's son al-Muhtadi was passed over due to his youth, and his half-brother al-Mutawakkil () was chosen as the next caliph by a coterie of leading officials.

Early life Al-Wathiq was born on 18 April 812 (various sources give slightly earlier or later dates in 811–813), on the road to Mecca. His father was the Abbasid prince, and later caliph, al-Mu'tasim (), and his mother a Byzantine Greek slave (), Qaratis. He was named Harun after his grandfather, Caliph Harun al-Rashid (), and had the teknonym Abu Ja'far.

The early life of al-Wathiq is obscure, all the more since his father was initially a junior prince without prospects of succession, who owed his rise to prominence, and eventually to the caliphate, to his control of an elite private army of Turkic slave troops (). Harun ibn Ziyad is mentioned as his first teacher, and he learned calligraphy, recitation and literature from his uncle, Caliph al-Ma'mun (). Later sources nickname him the "Little Ma'mun" on account of his erudition and moral character.

When al-Mu'tasim became caliph, he took care for al-Wathiq, as his son and heir-apparent, to acquire experience in governance. Thus al-Wathiq was left in charge of the capital Baghdad in 835, when al-Mu'tasim moved north to found a new capital at Samarra. He is then mentioned in the account of al-Tabari as being sent to ceremonially welcome the general al-Afshin during his victorious return from the suppression of the revolt of Babak Khorramdin in 838 (in present-day Iran), and being left behind as his father's deputy during the Amorion campaign of the same year.

Al-Wathiq is then mentioned in 841 as bringing a bowl of fruit to al-Afshin, now disgraced and imprisoned. Fearing that the fruit was poisoned, al-Afshin refused to accept it, and asked for someone else to convey a message to the Caliph. In Samarra, al-Wathiq's residence was immediately adjacent to his father's palace, and he was a fixed presence at court. As historian John Turner remarks, these reports show al-Wathiq in the "role of a trusted agent of his father, which positioned him well to take over the reins of power". On the other hand, al-Wathiq was never given a military command and did not even participate in the Amorion campaign, in a departure from previous Abbasid practice.

Reign Al-Tabari records that al-Wathiq was of medium height, handsome and well-built. He was fair with a ruddy complexion, commonly associated with noble descent. His left eye was paralyzed with a white fleck, which reportedly lent his gaze a stern aspect. When al-Mu'tasim died on 5 January 842, al-Wathiq succeeded him without opposition. Inheriting a full treasury, the new caliph made generous donations to the common people, especially in Baghdad and the Islamic holy cities of Mecca and Medina. Al-Wathiq sent his mother, Qaratis, accompanied by his brother Ja'far (the future caliph al-Mutawakkil), to head the pilgrimage in 842. Qaratis died on the way at al-Hirah on 16 August 842, and was buried in Kufa.

Ruling elites and Government Al-Wathiq's reign was short and is generally considered to have been essentially a continuation of al-Mu'tasim's own, as the government continued to be led by men that had been raised to power by al-Mu'tasim: the Turkic military commanders Itakh, Wasif, and Ashinas, the vizier, Muhammad ibn al-Zayyat, and the chief (judge), Ahmad ibn Abi Duwad. These men had been personally loyal to al-Mu'tasim, but were not similarly bound to al-Wathiq; in practice, according to Turner, this narrow circle "controlled the levers of power and thus the Caliph's independence".

In a gesture likely aimed at cementing an alliance between the caliph and his most powerful commander, al-Wathiq bestowed a crown on Ashinas in June/July 843, and on the occasion invested him with sweeping authority over the western provinces, from Samarra to the Maghreb—an act which the 15th-century Egyptian scholar al-Suyuti considered as the first occasion when royal power () was delegated by a caliph to a subject. Ashinas died in 844, and Itakh succeeded him in his rank as commander-in-chief and in his over-governorship of the western provinces. The new caliph also engaged in much construction in Samarra, which went a long way towards making the caliphal residence a proper city, with markets and a port adequate to its needs. This made Samarra not only more comfortable for its inhabitants but also made investment in property there economically attractive—both major considerations for the Abbasid elites and the military, who had been forced to relocate to the new capital by al-Mu'tasim.

However, in 843/44, the Caliph—allegedly at the instigation of the vizier Ibn al-Zayyat, or, according to a story reported by al-Tabari, inspired by the downfall of the Barmakids under Harun al-Rashid—arrested, tortured, and imposed heavy fines on several of the secretaries in the central government, in an effort to raise money to pay the Turkic troops. The measure was at the same time possibly aimed at driving a wedge between civilian and military elites, or at reducing the power of the leading Turkic commanders, such as Itakh and Ashinas, since most of the secretaries arrested and forced to pay were in their service.

Al-Haruni palace was built by al-Wathiq on the Tigris. It was named after his own given name Harun, He resided there during his reign, thus Al-Haruni was the main headquarter of his government in the capital city.

Suppression of rebellions

Already during the last months of al-Mu'tasim's life, a large-scale revolt had erupted in Palestine under a certain al-Mubarqa. Al-Mu'tasim sent the general Raja ibn Ayyub al-Hidari to confront the rebels. When al-Wathiq came to power, he dispatched al-Hidari against Ibn Bayhas, who led a Qaysi tribal revolt around Damascus. The exact relationship of this uprising with the revolt of al-Mubarqa is unclear. Taking advantage of the dissensions among the tribesmen, al-Hidari quickly defeated Ibn Bayhas, and then turned south and confronted al-Mubarqa's forces near Ramla. The battle was a decisive victory for the government army, with al-Mubarqa taken prisoner and brought to Samarra, where he was thrown into prison and never heard of again.

Upon coming to the throne, al-Wathiq appointed Khalid ibn Yazid al-Shaybani as governor of the restive province of Armenia. At the head of a large army, Khalid defeated the opposition of the local Muslim and Christian princes at the Battle of Kawakert. Khalid died soon after, but his son, Muhammad al-Shaybani, succeeded him in office and continued his father's task.

In spring 845, another tribal rebellion broke out. A local tribe, the Banu Sulaym, had become embroiled in a conflict with the tribes of Banu Kinanah and Bahilah around Medina, resulting in bloody clashes in February/March 845. The local governor, Salih ibn Ali, sent an army against them comprising regular troops as well as citizens of Medina, but, the Sulaym were victorious and proceeded to loot the environs of the two holy cities. As a result, in May al-Wathiq charged one of his Turkic generals, Bugha al-Kabir, to handle the affair. Accompanied by professional troops from the , Turkic, and guard regiments, Bugha defeated the Sulaym and forced them to surrender. In early autumn, he also forced the Banu Hilal to submit. Bugha's troops took many prisoners, some 1,300 in total who were held in Medina. They tried to escape, but were thwarted by the Medinese, and most were killed in the process. In the meantime, Bugha used the opportunity to intimidate the other Bedouin tribes of the region, and marched to confront the Banu Fazara and the Banu Murra. The tribes fled before his advance, with many submitting, and others fleeing to al-Balqa. Bugha then subdued the Banu Kilab, taking some 1,300 of them as prisoners back to Medina in May 846.

A minor Kharijite uprising in 845/6 occurred in Diyar Rabi'a under a certain Muhammad ibn Abdallah al-Tha'labi (or Muhammad ibn Amr), but was easily suppressed by the governor of Mosul. In the same year, the general Wasif suppressed restive Kurdish tribes in Isfahan, Jibal and Fars.

In September 846, al-Wathiq sent Bugha al-Kabir to stop the depredations of the Banu Numayr in Yamamah. On 4 February 847, Bugha fought a major engagement against about 3,000 Numayris at the watering place of Batn al-Sirr. At first he was hard pressed, and his forces almost disintegrated. Then some troops he had out raiding the Numayris' horses returned, fell upon the forces attacking Bugha and completely routed them. According to one report, up to 1,500 Numayris were killed. Bugha spent a few months pacifying the region, issuing writs of safe-passage to those who submitted and pursuing the rest, before he returned to Basra in June/July 847. Over 2,200 Bedouin from various tribes were brought captive with him.

Religious policy

Like his father, al-Wathiq was an ardent Mu'tazilite—the sources agree that he was strongly influenced by the chief , Ibn Abi Duwad—but also, like his father, maintained good relations with the Alids. In the third year of his caliphate, al-Wathiq revived the inquisition (), sending officials to question jurists on their views on the controversial topic of the createdness of the Quran. Al-Wathiq supported the Mu'tazili view that the Quran was created and not eternal, and hence fell within the authority of a God-guided imam (i.e., the caliph) to interpret according to the changing circumstances. Even during a prisoner exchange held with the Byzantine Empire in 845, the ransomed Muslim prisoners were questioned on their opinions regarding the topic, with those giving unsatisfactory answers reportedly left to remain in captivity. Thus Ahmad ibn Hanbal, the founder of the Hanbali school of jurisprudence, who opposed the Mu'tazili doctrine, was forced to cease his teachings and only resumed them after al-Wathiq's death. The abortive coup of al-Khuza'i and theft in public treasury (bayt al-mal) of Samarra