His killing of Hormuzan, whom he suspected of involvement in his father's assassination in 644, and his pardon by Caliph Uthman (r. 644–656) was opposed by Ali, the cousin of the Islamic prophet Muhammad.

Ubayd Allah was a son of Umar ibn al-Khattab, a companion of the Islamic prophet Muhammad and a member of the Banu Adi clan of the Quraysh tribe of Mecca who ruled as caliph from 634 until his assassination in 644.

[2] He was also married to Bahriyya, the daughter of Hani ibn Qabisa, a distinguished Arab commander at the Battle of Dhi Qar (609) who hailed from the Rabi'a tribe.

[5] Ubayd Allah also killed Jufayna, a Christian from al-Hira who served as a tutor for the children of the Muslim leader Sa'd ibn Abi Waqqas, and the young daughter of Abu Lu'lu'a.

[5] Umar's successor, Uthman (r. 644–656), pardoned Ubayd Allah, considering his execution as an excessive measure in view of his father's assassination;[6] he instead accepted blood money, which he paid out of his own funds.

[15]Because of his descent from Umar and the consequent connection to the "glorious early caliphate", Ubayd Allah's death represented a blow to Mu'awiya's prestige, according to the historian Wilferd Madelung.

[3][16] When Mu'awiya ultimately prevailed in the civil war and became caliph in 661, he pressured the Bakr to hand over the sword; it was found to be in the possession of the Bakrite tribesmen Muhriz ibn Sahsah of Basra.