The propaganda in favour of Muhammad b. `Ali is sometimes referred to as `Abbasid because he was descended from al-`Abbas, one of the three sons of `Abdu l-Muttalib, and so brother of Abu Talib the father of the Imam `Ali and of `Abdullah who was grandfather of the Prophet Muhammad. At the time, however, the missionaries claimed rather to be the supporters of the Hashimites, a term which was ambiguous, perhaps intentionally so. It was afterwards explained as referring to the house of Hashim which was the rival clan of the Quraysh opposed to the `Umayyads and that to which the Prophet, and `Ali, and al-`Abbas belonged: but in the minds of many of the Shi`ites it was taken to mean the followers of Abu Hashim, the grandson of Al-Hanafiya.
Muhammad b. `Ali died in 126 A.H. leaving three sons, Ibrahim, Abu l-Abbas, and Abu Ja`far, the first of these being recognised as his successor. About the same time Abu Muslim, who became governor of Khurasan in 129 comes into prominence. It is dubious whether he was an Arab or a native of `Iraq (cf. Masudi. vi. 59), indeed, the claim was made that he was a descendant of Gandarz, one of the ancient kings of Persia (id.) Now Khurasan was the area most disaffected towards the `Umayyads, and there the Hashimite missionaries had been most active and successful. Abu Muslim threw himself into this work heartily and began gathering together an armed body of men who before long numbered 200,000. Information and warning was sent to the Khalif Marwan II. but was ignored: indeed the court at Damascus took no notice until 130. Abu Muslim at length openly raised the black standard as the signal of revolt against the `Umayyads whose official colour was white. Then all the Khalif did was to seize Muhammad b. `Ali’s son Ibrahim and put him to death. The other two sons escaped and fled to Kufa where they were sheltered and concealed by some Shi`ites, the second son Abu l-`Abbas, known to history as _as-Saffah_ “the butcher” being recognised as the Hashimite leader.
Abu Muslim’s success was rapid and complete, and in 132 the `Umayyad dynasty was overthrown and partly exterminated, and so “the butcher” became the first of the `Abbasid Khalifs, so called as being of the family of al-`Abbas the son of `Abdu l-Muttalib.