60-1 Al-Hakim Abu Ali Al-Husayn ibn Ahmad al-Bayhaqi narrated that Muhammad ibn al-Sowli quoted on the authority of Oun ibn Muhammad, on the authority of Abul Husayn Muhammad ibn Abi Abbad - the one who was hired by Fadhl ibn Sahl to write for Imam Ar-Ridha’ (a.s.), “Ar-Ridha’ (a.s.) would never mention the name of his son Muhammad (a.s.) except by using his nickname (Abu Ja’far). For example, Ar-Ridha’ (a.s.) would say, ‘Abu Ja’far has written me a letter’ or say, ‘I wrote such and such to Abu Ja’far.’ This was so, even though his son was still a small child in Medina. However, the Imam (a.s.) always addressed him with respect. Abu Ja’far (a.s.) would also always respond in an extremely eloquent and charming manner. Once I heard Imam Ar-Ridha’ (a.s.) say, ‘Abu Ja’far (a.s.) is my Testamentary Trustee, and my successor from amongst my family after me.’”