Ubayd Allah ibn Umar

Ubayd Allah ibn Umar عُبَيْدِ اللَّهِ بْنُ عُمَرَ
Born	Unknown year
Died	657 Siffin, Syria
Burial place	Khalid ibn al-Walid Mosque, Homs, Syria (purported)
Spouses	Asma bint Utarid ibn Hajib al-Darimiyya Bahriyya bint Hani ibn Qabisa
Parents	Umar ibn al-Khattab (father) Umm Kulthum Mukayka bint Jarwal al-Khuza'iyya (mother)
Family	Banu Adi; Family of Umar
Military career
Allegiance	Mu'awiya I
Battles / wars	First Fitna Battle of Siffin †

Ubayd Allah ibn Umar ibn al-Khattab (Arabic: عُبَيْدِ اللَّهِ بْنُ عُمَرَ بْنُ الْخَطَّاب, romanized: ʿUbayd Allāh ibn ʿUmar ibn al-Khaṭṭāb; died summer 657) was a son of Caliph Umar (r. 634–644). 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. When Ali became caliph in 656, he refused Ubayd Allah's appeal to uphold Uthman's pardon, prompting Ubayd Allah to defect to Ali's principal enemy, the governor of Syria Mu'awiya ibn Abi Sufyan. The latter made Ubayd Allah a commander of his elite battalion at the Battle of Siffin, where he was slain.