It is stated in the sources that Imam Sadiq (AS) introduced five people, including the Abbasid Caliph, as his successors in view of the strictness of the Abbasids and to protect the life of Imam Kazim (AS). [Pishvai, Sirah Pishvaiyan, 1372, p. 414]

Although Imam Sadiq (AS) had repeatedly introduced the Imam after him to his special companions, this action somewhat confused the situation for the Shiites. During this period, some of the prominent companions of Imam Sadiq (AS) such as Momin Taq and Hisham bin Salim were also in doubt. They first went to Abdullah Aftah, who had claimed to be the Imam, and asked him about zakat. But Abdullah's answers did not convince them. The two then met with Musa ibn Ja'far (a.s.) and were satisfied with his answers and accepted his imamate. [Kashshi, Rijal, 1409 AH, pp. 282-283]