 Complete the following phrase:  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 