ʿUyūn akhbār al-Riḍā 1, narration 81

Translation

7-2 Al-Hussein ibn Ibrahim ibn Ahmad ibn Hisham al-Mu’addib - may God be pleased with him - narrated that Ali ibn Ibrahim ibn Hashem quoted on the authority of Muhammad ibn Isa ibn Obayd, on the authority of Musa ibn Al-Qasim al-Bajali, on the authority of Ali ibn Ja’far (s), “Muhammad ibn Isma’il ibn Ja’far ibn Muhammad (Imam Kadhim’s brother) came to me and said, “Muhammad ibn Ja’far went to see Harun Ar-Rashid and greeted him as the Caliph. He then told him, ‘I did not think that there were two Caliphs on the Earth until I saw that they greet my brother Musa ibn Ja’far as the Caliph.’”One of the people who said bad things behind Musa ibn Ja’far’s (s) back was Yaqoob ibn Dawood. He was one of the Zaydites.

Translation: Dr. Ali Peiravi — published with the edition, reproduced verbatim.