Al-Saffah was a great-grandson of Abbas ibn Abd al-Muttalib, an uncle of the Islamic prophet, Muhammad. Al-Saffah began asserting his claim to become caliph in the 740s and became particularly active in Khorasan, an area where non-Arab Muslims lived. After the death of the Umayyad caliph Hisham ibn Abd al-Malik in 743 a period of instability followed. Al-Saffah led the Abbasid Revolution in 747 and his claim to power was supported throughout Iraq by Muslims. He became the first caliph of the Abbasid caliphate in 750 after defeating his rivals.