Imam Riḍā’s (P.B.U.H.) Journey to Khurāsān
After consulting Faḍl, Maʿmūn came up with a treacherous plan. He decided to offer the caliphate to Imam Riḍā (P.B.U.H.) and withdraw himself.  Because whether the Imam (P.B.U.H.) accepted or not, it would still be a victory for Maʿmūn. If Imam (P.B.U.H.) accepted, and became caliph allowing for Maʿmūn to be the vice-caliph, that would guarantee the legitimacy of Maʿmūn’s government. Thus Maʿmūn decided to force the position of caliph on Imam (P.B.U.H.). It was then easier for him to eliminate Imam Riḍā (P.B.U.H.) and become the legal leader. In this case, the Shiʿites would consider his government to be legitimate and would be satisfied with it and accepted him as Imam’s (P.B.U.H.) successor.  Furthermore, the risings made against his government would lose their attraction and legitimacy.
However, if Imam (P.B.U.H.) didn’t accept the caliphate, he would then oblige Imam (P.B.U.H.) to be his successor and guarantee the legitimacy of his government through this to weaken the uprisings. On the other hand, he could make Imam (P.B.U.H.) settle near himself to control him and suppress his followers. In addition, Imam Riḍā’s (P.B.U.H.) Shiʿites and followers would criticize him for not accepting the caliphate and he would lose his respect among them.
To accomplish his mentioned goals, Maʿmūn sent some of his especial agents to Imam Riḍā (P.B.U.H.) in Medina to force him to set on a journey to Khurāsān. He also ordered to take Imam Riḍā (P.B.U.H.) through a path that has the least number of Shiʿites. The main roads in those days were the roads to Kufa, Jabal, Kermanshāh, and Qum, which were all mainly Shiʿite cities.  It seemed probable to Maʿmūn that Shiʿites may get excited when they see Imam (P.B.U.H.) and prevent him to continue his travel to stay with them instead.  To prevent these troubles, Maʿmūn made Imam Riḍā (P.B.U.H.) travel through the paths of Baṣra, Ahvāz, and Fārs to Marv. His agents also watched Imam (P.B.U.H.) continuously and reported to Maʿmūn on all of Imam’s (P.B.U.H.) activities.