The situation brought about for Imam Ali b. Mūsā al-Riḍā (A.S.) in comparison to other Imams is of special features, because after Imam Ali (A.S.) it was only for him from among this household that the entering the caliphate system was made possible. It was this very factor that both sublimated the status of the Imam and prompted some questions as well. One of these questions is that whether the person behind the invitation of the Imam to Iran was Ma‘mūn himself or Faḍl b. Sahl? In both instances, was their objective in this matter to serve the religion and reinforce the Sh‘ī culture or was their action a deceiving plot, which each one of them had planned and executed for achieving their own purposes? Given various hypotheses in this respect, this research is intended first to introduce the existing hypotheses and explain and criticize them with reasons provided, and then by mentioning strong reasons and historical evidences, prove the possibility that the coming of the Imam to Merv was by the invitation of Ma‘mūn himself.
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