ʿAbd Allāh fought under Ṣaʿd ibn Abī Waḳḳāṣ in the conquest of Iraq. In the first Muslim civil war, he took the side of the Caliph ʿAlī and fought for him at the Battle of Ṣiffīn (657). He opposed ʿAlī's decision to accept arbitration to end the civil war and joined the dissidents, soon to be known as Khārijites, gathering at Ḥarūrāʾ in Iraq. They later moved to Kūfa, where they elected ʿAbd Allāh as their "amīr" (commander) and not, as is sometimes claimed, the true caliph (successor of Muḥammad). They marched out in March 658 and were routed by ʿAlī in the Battle of Nahrawān on 17 July (9 Ṣafar 38 AH). ʿAbd Allāh was killed in battle.