The Abbasids, rivals of the Umayyads, are members of the Hashim clan, but the word "Hashimiyya" seems to refer specifically to Abu Hashim, a grandson of Ali and son of Muhammad ibn al-Hanafiyya.

Hashimiyya missions beginning around 719 had begun to seek adherents in Khorasan, their campaign framed as one of proselytism (dawah).

They seek support for a "member of the family" of Muhammad, without making explicit mention of the Abbasids.

These missions meet with success both among Arabs and non-Arabs (mawali), although the latter may have played a particularly important role in the growth of the movement.

Abu Muslim around 746 assumes leadership of the Hashimiyya in Khorasan.

He successfully initiates an open revolt in 747, organized under the sign of the black flag, against Umayyad rule.

He soon establishes control of Khorasan, expelling its Umayyad governor, and dispatches an army westwards.