Muhammad ibn Salih ibn Bayhas al-Kilabi, better known as Ibn Bayhas (Arabic: أبن بيهس), was the Abbasid governor of Damascus in September 813–824/825 and a prominent chief of the Qays tribes in the environs of Damascus against their Yamani rivals. Under his leadership, a succession of Umayyad claimants to the caliphate, Abu al-Umaytir al-Sufyani, Maslama ibn Ya'qub al-Marwani and Sa'id ibn Khalid al-Uthmani, were defeated, marking an end to serious challenges of Abbasid authority in Syria by remnants of the Umayyad dynasty, which had been toppled by the Abbasids in 750. Although a loyalist of Caliph al-Ma'mun, he was viewed as a rival by al-Ma'mun's viceroy of Syria, Abd Allah ibn Tahir ibn al-Husayn, who deposed him around 824/825. Two years later, he was brought to Iraq, where he eventually died.

Ibn Bayhas was the son of Salih ibn Bayhas, who, in 800, was sent by the Abbasid caliph Harun al-Rashid to the Byzantine empress Irene in Constantinople to ransom Muslim prisoners-of-war.^[1][2] Salih's brother Kardam had been the Umayyad governor of Oman. Their father, Bayhas ibn Zumayl, was a noble (sharif) of the Banu Kilab tribe in Damascus. He served as the seal-bearer of the Umayyad caliph al-Walid II and witnessed the latter's assassination in 743, which sparked the Third Muslim Civil War.^[2]

Ibn Bayhas was a tribal chief, warrior and poet.^[1] He became "a key power broker" in Syria, according to the historian Wilferd Madelung.^[1] He was viewed by his Qaysi tribal partisans as their champion against theirs rivals, the Yaman–Banu Kalb. The Qays–Yaman rivalry for power and influence in Syria dated to the early Umayyad period in the 680s and remained potent during Abbasid rule, which began in 750. Unlike most of his Qaysi brethren in Syria, who opposed the Abbasids, Ibn Bayhas was an Abbasid loyalist and did not support the remnants of the Umayyad dynasty in the region and their supporters, who on several occasions attempted to expel the Abbasids.^[1]

The pro-Umayyads in Syria attempted to gain power during the political chaos of the Fourth Muslim Civil War, which pitted the Abbasid contenders for the caliphate, Caliph al-Amin and his brother al-Ma'mun, sons of Harun al-Rashid, against each other. The Abbasid governor of Syria, Sulayman ibn Abi Ja'far, imprisoned Ibn Bayhas in a dungeon inside the Palace of al-Hajjaj, where the governor resided. Sulayman may have been persuaded to arrest Ibn Bayhas by the pro-Umayyad conspirators, who at this point were operating clandestinely. The pro-Umayyad faction raised support from Yamani and Qaysi tribesmen and affiliates, but feared that the ardently pro-Abbasid Ibn Bayhas would not come to their side. They resolved to neutralize him by convincing the Abbasid governor that Ibn Bayhas was a leader of the Zawaqil, desert brigands who were devastating the Syrian countryside during the civil war.^[3]

Soon after Ibn Bayhas was imprisoned, the pro-Umayyad rebellion was launched, with a descendant of the Umayyad caliph Mu'awiya I (r. 661–680), Abu al-Umaytir, at the helm. The rebels besieged Sulayman in his palace, prompting him to free Ibn Bayhas in return for safely escorting him out of Damascus. Ibn Bayhas and his horsemen secured Sulayman's escape through the Hauran, accompanying him as far Thaniyyat al-Uqab in the Syrian Desert before parting ways;^[4] Sulayman returned to Iraq while Ibn Bayhas headed back to the Hauran.^[5] Large parts of Syria, namely Damascus, the Beqaa Valley, most of the coastal cities, such as Sidon, and Jund Hims (district of Homs), came under Abu al-Umaytir's authority.^[6] Al-Amin dispatched a son of his general Ali ibn Isa ibn Mahan to suppress the Syrian rebellion, but he halted at the city of Raqqa in the Jazira, the province bordering Syria to the northeast. This was possibly due to concerns that Ibn Bayhas, the Abbasids' main ally in Syria at this time, was a supporter of al-Ma'mun.^[7]

Abu al-Umaytir invited Ibn Bayhas to back his revolt, but he refused. Instead, Ibn Bayhas rallied tribesmen from the Dibab, the branch of the Banu Kilab to which he belonged, the Banu Numayr, and his mawali (non-Arab clients or freedmen) and headed for Damascus to relieve the Qays there from the persecutions of Abu al-Umaytir's largely Yamani following. Abu al-Umaytir sent against him an Umayyad kinsman, who routed Ibn Bayhas's forces in the Hauran, causing them to disperse to different parts of Syria, with the Banu Murra chief Sadaqa ibn Uthman fleeing for Tiberias and another Qaysi chief, Umara, retreating to Adhri'at (modern Daraa). The tide turned against the Umayyads when, upon the Umayyad force's return to Damascus, they were ambushed by local villagers or nomads affiliated with the Qays. Ibn Bayhas took advantage, gathering his men and leading a charge which brought them to the gates of Damascus. Ibn Bayhas remained encamped in the Ghouta gardens, which surround Damascus, attacking anyone leaving or entering the city.^[8] Abu al-Umaytir called on his Yamani supporters from the Beqaa, Baalbek and Sidon to relieve the siege, whereupon tens of thousands of his loyalists arrived and engaged in a heavy battle with the Qaysi besiegers. Both sides suffered heavy losses and Ibn Bayhas was forced to retreat to the Hauran. The death of Abu al-Umaytir's son, al-Qasim, during the battle spurred Abu al-Umaytir to send his troops against Ibn Bayhas, but they were defeated.^[9]

The victory of Ibn Bayhas in the Hauran significantly weakened Abu al-Umaytir's position; however, Ibn Bayhas had fallen ill and could not lead his men on an attack against the Umayyad leader. Instead, he nominated another Umayyad, Maslama ibn Ya'qub, from the Marwanid line of the Umayyad dynasty, which historically had been closely identified with the Qays, to lead them. The Banu Numayr gave Maslama their oath of allegiance and together they assaulted Damascus, arresting Abu al-Umaytir in his residence, the Green Palace. Maslama gained oaths of allegiance as caliph from the Umayyad family members and mawali in the city, while he rewarded the Qays with plots and pasturelands.^[9]

When Ibn Bayhas recovered he came to view Maslama as a threat and resolved to neutralize him. He gathered a Qaysi army which Maslama's own Qaysi partisans confronted at the city gates. The spectacle of Qaysi in-fighting may have caused the Qaysi supporters of Maslama to reconsider their allegiance; in the aftermath of the inconclusive battle, they secretly defected to Ibn Bayhas.^[10] With help from the Qaysi defectors inside Damascus, Ibn Bayhas's men scaled the Bab Kaysan gate and entered the city victoriously on 13 September 813.^[11] Maslama and Abu al-Umaytir had already escaped together and gained refuge in the Yamani villages of the Ghouta.^[10]

Shortly after capturing Damascus, Ibn Bayhas was recognized as governor of Jund Dimashq (the military district of Damascus) by al-Ma'mun, who had by then defeated and succeeded al-Amin.^[12] He restored the properties expropriated and redistributed by the Umayyad counter-caliphs to their previous owners, including to the members of the Banu Hashim (the clan to which the Islamic prophet Muhammad and the Abbasids belonged) and their mawali who had fled Umayyad rule.^[13] He minted silver dirhams in the city, inscribed in his and al-Ma'mun's name, which marked the first time Abbasid coins were minted in Damascus. His associate, al-Harith ibn Isa, assumed control of the port of Tyre and supervised its harbor of warships.^[12]

Although he governed with the recognition of the Abbasids, Ibn Bayhas ruled "purely on his own" and worked to strengthen the Qaysi position in the district at the expense of the hitherto dominant Yaman, according to the historian Paul Cobb.^[13]