The threat imposed on the caliphate system…
The threat imposed on the caliphate system by Imam Musa Ibn Ja’far al-Kadhim (A) was that of a great leader with extensive knowledge [and] he was so courageous that he feared no power against him. Such a personality – Mubarez, a fighter on the path of Allah, connected with Allah, who relied upon Allah, having friends all over the Islamic World, and having a plan for setting up an Islamic government and an Islamic system – was a great threat to the Harunid (Abbasid) government. Thus, Harun [al-Rashid] decided to get rid of this threatening presence.