Abū al-ʿAbbās Aḥmad ibn Muḥammad ibn Muḥammad al-Mustaʿīn bi-ʾllāh (Arabic: أبو العباس أحمد بن محمد بن محمد; 836 – 17 October 866), better known by his regnal title al-Mustaʿīn, was the Abbasid caliph from 862 to 866 during the period known as the "Anarchy at Samarra". Following the death of caliph al-Muntasir, the Turkic military leaders bypassed the claims of al-Mu'tazz and his brothers and selected al-Mustaʿīn, a nephew of al-Mutawakkil, as caliph.
Al-Mustaʿīn's reign was marked by the growing influence of the Turkish military officers in the affairs of the caliphate. His accession provoked unrest in Samarra and opposition from supporters of al-Mu'tazz, while defeats in campaigns in Armenia and Asia Minor and internal rebellions contributed to instability within the caliphate. In 865, conflict between rival military factions led al-Mustaʿīn to flee from Samarra to Baghdad, where he became the center of a civil war with al-Mu'tazz and his supporters.
After a prolonged siege of Baghdad, al-Mustaʿīn agreed to abdicate in favor of al-Mu'tazz in January 866. Although he was promised safe conduct and retirement in the Hijaz, he remained under guard in Baghdad and was executed later that year on the orders of al-Mu'tazz.
Ahmad ibn Muhammad (future al-Musta'in) was the son of Abbasid prince Muhammad ibn al-Mu'tasim and his mother was a concubine from province of Sicily called Makhariq. Al-Musta'in was the grandson of caliph al-Mu'tasim (r. 833–842). He was the nephew of caliph al-Wathiq (r. 842–847) and caliph al-Mutawakkil (r. 847–861).
His uncle, caliph al-Mutawakkil (r. 847–861) had created a plan of succession that would allow his sons to inherit the caliphate after his death; he would be succeeded first by his eldest son, al-Muntasir, then by al-Mu'tazz and third by al-Mu'ayyad. In December 861 al-Mutawakkil was assassinated by a group of Turkic military officers, likely with the support of al-Muntasir. During al-Muntasir's short reign (r. 861–862), the Turks pressured him into removing al-Mu'tazz and al-Mu'ayyad from the succession. When al-Muntasir died, the Turkic officers gathered together and decided to install the dead caliph's cousin al-Musta'in on the throne.
Following al-Muntasir's death in June 862, Utamish and the officers Bugha al-Kabir and Bugha al-Sharabi met to select a new caliph, eventually deciding on al-Musta'in, a nephew of al-Mutawakkil. Utamish seems to have held a strong influence on al-Musta'in and became one of the most powerful individuals in the new administration; he was appointed as vizier and given control over the treasury, and additionally received the governorships of Egypt and the Maghrib. Al-Musta'in further entrusted him with the supervision of his son al-Abbas.
The new caliph was almost immediately faced with a large riot in Samarra in support of the disenfranchised al-Mu'tazz; the rioters were put down by the military but casualties on both sides were heavy. Al-Musta'in, worried that al-Mu'tazz or al-Mua'yyad could press their claims to the caliphate, first attempted to buy them off and then threw them in prison.
The governor of Baghdad persuaded the city to submit, and the succession was thereafter acknowledged throughout the land. Al-Mu'tazz and his brother, threatened by the Turkic and Berber troops, resigned their titles to succeed, and were then, by way of protection, kept in confinement. After a second attempt to overturn the decision made by the Turks, al-Mu'tazz and his brother would have been put to death, but the vizier intervened and saved their lives, for which act of mercy, his property was seized by the Turkic soldiers, and himself banished to Crete. The Empire, in fact, both at home and abroad, had passed into the hands of Turks.
Over the course of the first year of al-Musta'in's reign, Utamish enjoyed influence over the caliph and his affairs; in the opinion of the historian Dominique Sourdel, he was "un véritable régent de l'empire." As vizier, he seems to have managed little of the day-to-day administration, leaving his secretary Shuja' ibn al-Qasim to handle it instead. Utamish and Shuja' seem to have initially shared power with Ahmad ibn al-Khasib, until the latter was exiled in July 862.
During his reign, al-Musta'in also married-off Najla, a concubine of his dead uncle Al-Mutawakkil to the Utamish. She was known for her beauty and singing.
In 863, the Muslim campaign against the Christians was going badly. Two whole corps in Armenia and Asia Minor, some 8,000 strong, with their leaders, were killed during the Battle of Lalakaon. The tidings created anger and riots in Baghdad. The ancient cry for a Holy War rang through the streets. People blamed the Turks that had brought disaster on the faith, murdered their Caliphs, and set up others at their pleasure.
With such cries the city rose in uproar; the prisons were broken into and bridges burned. But Baghdad could no longer dictate to its rulers; it could only riot. The fighting spirit was, however, strong enough to draw men from the surrounding provinces, who flocked as free lances to fight against the infidel. But the Turks cared for none of these things, nor did the Caliph.
In 864, his forces put down a rebellion by the Alid Yahya ibn Umar and a revolt in Hims.
Utamish's influence over the government soon caused him to make enemies in the army and bureaucracy. He and several other officials stole from the treasury, which caused discontent among the poorly-paid mawlas. Utamish also excluded the influential officers Bugha al-Sharabi and Wasif al-Turki from power, and the two retaliated by plotting his downfall. On June 4, 863, the Turks and Faraghina marched out from their cantonments in Samarra and advanced toward the Jawsaq Palace against Utamish. The vizier attempted to seek refuge with al-Musta'in but was refused; two days later, the troops entered the palace and seized Utamish. He and Shuja' were killed and Utamish's residence was plundered.
In 865, the end for al-Musta'in himself was now at hand. After some disagreements between the Turkish leaders that placed al-Musta'in in much danger, he, along with two other Turkic leaders, Bugha al-Sharabi (known as Bugha al-Saghir) and Wasif al-Turki, left Samarra on a boat to East Baghdad. The Turks sent after him a party of their captains, requesting him to return to Samarra. But the Caliph refused, and hard words followed between the two sides, in the heat of which one of the Turkic speakers received a blow.
The insult rankled the Turkic officers, and on returning to Samarra, the Turkic troops rose together, and bringing forth al-Mu'tazz from his confinement, saluted him as Caliph. Within a few weeks, his brother Abu Ahmad al-Muwaffaq, with 50,000 Turks and 2,000 Berbers, besieged Baghdad, a siege that would last throughout the year 865.
Abdication in favor of al-Mu'tazz
As the siege of Baghdad wore on, it began to have its intended effect. Food and money slowly became scarce, and discontent among the populace began to emerge. As early as August, a group of members of the Abbasid family complained to Muhammad ibn 'Abdallah that their stipends were not being paid. As conditions in the city deteriorated, Muhammad gradually became convinced that victory through force of arms was impossible. By November at the latest, and without the knowledge or permission of al-Musta'in, he had opened negotiations with al-Mu'tazz regarding al-Musta'in's surrender.