His followers later developed into a distinct Shi'a sect known as the Kaysanites. They introduced the doctrines of Occultation (Ghayba) and Return (Raj'a) of the Mahdi. After the death of Ibn al-Hanafiyyah, some Kaysanites believed that he had not died but was hidden in Mount Radwa and would return some day to rid the world of injustice. Most Kaysanites, however, declared his son Abu Hashim to be their Imam. He then transferred the Imamate to Muhammad ibn Ali ibn Abdallah ibn Abbas before dying. The Abbasids used this as a propaganda tool during their revolution to boost their legitimacy and appeal to pro-Alid masses. Two of Muhammad ibn Ali's sons, as-Saffah and al-Mansur, would eventually establish the Abbasid Caliphate. Describing similarities between Mukhtar and Abbasid revolutionary Abu Muslim Khorasani, who recruited both Arabs and "mawali" in his army and treated them as equals, Wellhausen writes: "If the doctrine of Raj'a is correct, then the Arab of Khutarnia [Mukhtar] came to life again in the Maula ["mawlā"] of Khutarnia [Abu Muslim]."