Sufyan ibn Nazar says: One day, we were with Mamun when he said, “Do you know from whom I learned Shi’ism?” Everyone replied, “No, by God, we do not know.” Mamun said, “I learned it from my father, Harun al-Rashid.” We asked, “How is that possible, while Harun was killing members of this family?” Mamun responded, “He killed them for the sake of the kingdom and the throne, to ensure that his rule would not remain incomplete. However, one year, I went on Hajj with him. When we reached Medina, he entered his tent and ordered that no one from the people of Medina or Mecca, whether from the Muhajirun (migrants), Ansar, Banu Hashim, or any other tribe of Quraysh, should visit him unless they state their lineage. So, people came and stated their lineage, tracing it back to their ancestor from either the Quraysh, the Muhajirun, the Ansar, or Banu Hashim. Then Harun would gift them between two hundred and five thousand dinars, depending on the nobility of their lineage and their ancestors’ emigration.”
“One day, I was standing when Fadl ibn Rabi came and said, ‘A man has arrived, claiming to be Musa ibn Ja’far (peace be upon him), and his lineage goes back to Ali ibn Abi Talib (peace be upon him).’ I, Amin, Mu’tamin, and other leaders were there. Harun turned to us and said, ‘Pay attention and be cautious in your behavior.’ Then he allowed him to enter, saying, ‘I will take him into my court.’ A man entered, an elderly person with a yellowish complexion, his worship had weakened him so much that he looked like dried skin. His forehead and nose had calluses from prostrations. When he saw Harun, he wanted to dismount from the donkey he was riding, but Harun shouted, ‘No, come in mounted.’ He moved the curtain aside, and we all looked at him with respect and admiration. He rode to the court, surrounded by the courtiers. Then he dismounted, and Harun rushed to meet him, kissed his face, took him to the head of the assembly, and seated him beside himself. Then Harun started talking to him, kissing his face and greeting him.”
“He said to Harun: ‘God has made it obligatory for rulers to take care of the livelihood of the poor, to pay the debts of those who are unable to pay them, to give the rights of the impoverished, to clothe those who cannot afford clothing, and to show kindness to prisoners. It would be better if you attend to these matters as well.’ Harun replied, ‘We also do this, O Abu al-Hasan.’ Then the Imam stood up, and Harun also rose, kissed his hands, and said to me, Amin, and Mu’tamin, ‘Go with your cousin and master and accompany him to his home.’
“On the way, the Imam turned to me and, speaking softly so others could not hear, he congratulated me on my future caliphate and said, ‘When you come to power, treat my son well.’ I was the boldest of my brothers, and when we returned and the gathering became private, I asked him, ‘O Commander of the Faithful, who was that man whom you treated with such honor, standing up for him, kissing his hands, and seating him at the head of the assembly, while you sat below him? Then you ordered us to escort him and hold his stirrup.'”
“Harun replied, ‘That man is the Imam of the people, the proof of God upon His creation, and the Caliph of God over His servants.’ I said, ‘O Commander of the Faithful, do you not possess all these attributes as well?'”
“Harun replied, ‘I am the Imam of the people outwardly and by force, but Musa ibn Ja’far (peace be upon him) is the true Imam. By God, he is more deserving of the position of the Messenger of God (peace be upon him) than I and all of creation. By God, if you dispute this with me, I will take your life, and my kingship will remain childless.'”
“When he was about to leave Medina for Mecca, he ordered Fadl ibn Rabi to take a bag of money, which contained two hundred dinars, and go to Musa ibn Ja’far (peace be upon him). He should tell him, ‘The Commander of the Faithful says that we are currently short of funds, but we will give you more later.'”
“I said, ‘O Commander of the Faithful, you would give five thousand dinars to the children of the Muhajirun, the Ansar, and other Quraysh tribes, and even those whose lineage you did not know, and yet to Musa ibn Ja’far (peace be upon him), whom you have honored and respected so much, you only give two hundred dinars, the smallest amount you’ve given to anyone?'”
“Harun said, ‘Be silent. If I give him this money, there is no guarantee that tomorrow he won’t lead a hundred thousand of his Shi’ah and supporters against me. His poverty and the poverty of his family is safer for me and you than their wealth.'”
Source: ‘Uyun Akhbar al-Ridha’, Volume 1, Chapter 7, Page 88, by Sheikh Saduq