Imam Reza lived for 55 years, from which 35 years was before Imamate and in the reigns of Abbasid caliphs Mansur, Mahdi, Hadi, and Harun. His Imamate, lasting for twenty years, coincided with the tenure of Harun, Muhammed Amin, and Ma’mun. During his tenure, Harun never encountered the Imam due to the crises that the government faced, and this provided an opportunity for the Imam to educate more students and disseminate the teachings of Islam with greater ease. Ma’mun was the seventh Abbasid caliph, and the great issue that always worried Ma’mun was the privileged personality of Imam Reza (AS), which he considered a threat to his rule.
After taking the government, Ma’mun in a letter invited Imam Reza to visit Khorasan but he refused to go. However, Ma’mun insisted and sent letters of invitation one after another to show that he would not give up. Following repeated invitations, Ma’mun sent two of his people to Medina to take the Imam to Khorasan. When the Imam figured out that he had to emigrate to Khorasan, he went to the Holy Shrine of the Prophet (pbuh) several times and revealed his discontent with the journey, so that others would know that the Imam had been forced to travel. While leaving Medina, the Imam called all his relatives and told them, “Weep for me, because I will not return to Medina again”. Another testimony to Imam's reluctance and displeasure from the journey is the path determined by the caliphate, in such a way that he was taken secretly from certain areas and they prevented him from entering Kufa and Qum.
Imam Reza (AS) accepted the Abbasid caliph’s role of crown prince, and in an historic and unrepeated opportunity in the political scene, conversed with the religious leaders. This incident, which according to many of the Abbasid family figures, could remove the power out of their hands, and according to a number of devotees, was an affirmation of the reign, is worthy of consideration from various aspects.
As far as Imam Reza (AS) as the learned man of the Prophet’s household, decided to respond by recalling the presence of the truthful Joseph in the Pharaoh’s reign, he obliterated the doubt from minds. The Imam used every occasion to state the truth, expressing his dissatisfaction, and even used the opportunity of his prayers to reveal the truth, saying “O’ Lord, you know that I accepted the position of crown prince unavoidably and with reluctance, so do not reprimand me as you did not hold your Prophet Joseph accountable for the acceptance of Egypt’s reign”.
Accordingly, the most important event in the political life of the Imam that took place in Merv, was the acceptance of position of crown prince and after that Ma’mun minted a coin in his name and named him in sermons. Undeniably, position of crown prince was an opportunity. Some of the benefits included the following: Firstly, if the act went right, the caliphate would return to its original position, and people could taste the Prophetic wisdom and Imam Ali’s justice after several decades. Secondly, it was not necessary for the Imam's scientific and promotional activities to be hidden and only for a small number. Thirdly, this appointment was a healing for the deep wound on the body of the Islamic society, a wound caused by obvious oppression against the dearest son of the Prophet (pbuh), i.e. the martyrdom of Imam Hussein (AS) that not only was not healed, but a disgrace based on which everyday some rose up for vengeance, and they demanded the rule of Imam Reza (AS) from Prophet’s household. And fourthly, it was a reason to protect the mighty Islamic foundation against the danger of overthrow, an inevitable collapse that Harun had sowed with sharing property between Amin and Ma’mun.
Acceptance of the position of crown prince was under intense pressure and the Imam accepted it when the threats of Ma’mun became serious, as reluctance is clear from the text of the position of crown prince pledge (which is fortunately available in historical sources).
In Imam Reza's vision, the Imam is not solely responsible for the expression of the religious laws, but Imamate, if it is righteous, also leads the political and social aspects of the Islamic society. In any case, when the Imam was forced to accept position of crown prince, he decided to represent his virtuous image in a counted and cultural manner and these actions and his popularity among the various classes, from the public to the ministers and counselors, eventually scared Ma’mun and he decided to eliminate the Imam.