Succession to Caliphate
When Imam Riḍā (P.B.U.H.) entered Marv, Maʿmūn welcomed him royally and publicly through a speech in front of all the key characters of government. He said, “All should know that I do not know anyone better and more deserving on succession than ʿAlī b. Mūsā al-Riḍā (P.B.U.H.) in descendants of ʿAbbās or ʿAlī (P.B.U.H.)”. After that he turned his face to Imam (P.B.U.H.) and said, “I have decided to dethrone myself and announce you as the caliph”. Imam Riḍā (P.B.U.H.) said, “If Allah has specified caliphate for you then it is not permitted to give it to another one and if it is not yours then you do not have the authority to give it to another one.”
Maʿmūn insisted on what he wanted but Imam (P.B.U.H.) said, “Never will I accept that”. When Maʿmūn got disappointed, he told Imam (P.B.U.H.), “Then accept to be the caliph after me, and successor of me”. The insistence of Maʿmūn on his wants and Imam Riḍā’s (P.B.U.H.) refusal lasted for two month. He did not accept and said, “I have heard from my fathers that I will die before you and will be martyred with poison and angles of the earth and skies will cry for me and I will be buried in the land of nostalgia beside Hārūn al-Rashīd”. But Maʿmūn insisted on succession of Imam Riḍā (P.B.U.H.) in such way that he threatened Imam (P.B.U.H.) to death in a secret and private ceremony. Thus Imam said, “Now, since I am obliged, I accept it but on the condition that I do not appoint or depose anyone and do not change any custom or rule and control affaires imperceptibly”. Maʿmūn had no choice but to accept this condition.