The Shia narrations regarding the successorship of Imam Reza by Caliph Mamun contradict one another. The first report shows that Imam Reza was happy with it, and considered that Mamun did this out of good intentions and for the sake of Allah.
Shaykh Saduq records:
حدثنا الحاكم أبو علي الحسين بن أحمد البيهقي، قال حدثني محمد بن يحيى الصولي قال: حدثني أحمد بن محمد بن إسحاق قال: حدثنا أبي قال: لما بويع الرضا عليه السلام بالعهد اجتمع الناس إليه يهنئونه فأومى إليهم فانصتوا، ثم قال بعد أن استمع كلامهم: بسم الله الرحمن الرحيم الحمد لله الفعال لما يشاء لا معقب لحكمه ولا راد لقضائه (يعلم خائنة الأعين وما تخفي الصدور) وصلى الله على محمد في الأولين والآخرين وعلى آله الطيبين الطاهرين أقول وأنا علي بن موسى بن جعفر عليهما السلام: إن أمير المؤمنين عضده الله بالسداد ووفقه للرشاد عرف من حقنا ما جهله غيره، فوصل أرحاما قطعت وآمن نفوسا فزعت بل أحياها وقد تلفت وأغناها إذا افتقرت مبتغيا رضا رب العالمين لا يريد جزاء إلا من عنده (وسيجزي الله الشاكرين ولا يضيع أجر المحسنين) وأنه جعل إلي عهده والامرة الكبرى إن بقيت بعده فمن حل عقدة أمر الله تعالى بشدها وقصم عروة أحب الله إيثاقها فقد أباح حريمه وأحل محرمه إذا كان بذلك زاريا ( ١) على الامام منتهكا ( ٢) حرمة الاسلام، بذلك جرى السالف فصبر منه على الفلتات ولم يعترض بعدها على الغرمات خوفا على شتات الدين واضطراب حبل المسلمين ولقرب أمر الجاهلية ورصد المنافقين فرصة تنتهز وبائقة تبتدر وما أدري ما يفعل بي ولا بكم؟ أن الحكم إلا لله يقضي الحق
Al-Hakim Abu Ali Al-Hussein ibn Ahmad al-Bayhaqi narrated that Muhammad ibn Yahya al-Sowli quoted on the authority of Ahmad ibn Muhammad ibn Ishaq, on the authority of his father, “When they pledged allegiance to Al-Reza (s), the people gathered around him and congratulated him. He made a gesture to them to become silent and after hearing their words, he said, ‘In the Name of God, the Beneficent, the Merciful. Praise be to God who does whatever He wills. No one can object to His Decrees. No one can reject His Destiny. He knows whatever treason that lies in one’s heart from the sight and whatever is hidden in the hearts. May God’s Blessings be upon Muhammad, upon the first and the last creatures, upon his good and pure Household.’ He then added, ‘I am Ali ibn Musa ibn Ja’far. Indeed the Commander of the Faithful (Al-Ma’mun) – may God assist him in righteousness and make him successful in being rational – has recognized one of our rights which others were ignorant about. He has established ties of kinship which others have broken. He has granted security to people who lived in fear. He even revived them and rescued them from destruction. He enriched them when they were in need. He was seeking the pleasure of the Lord of the Two Worlds in doing all this. He did not ask anyone but Him to reward him. God will reward the ones who are grateful. He will not let the reward of the good-doers be forgotten. He turned over the succession to the throne to me. He has entrusted his great rule to me after him. And whoever breaks a contract that God has ordered to be safeguarded, and loosens ties which God likes to be tightened has indeed underestimated God’s Bounds, and has allowed what God has forbidden. In this way, he has denied the leader of his right and has disobeyed his orders. He has thus disrespected Islam as was done in the past. The Trustee (Ali ibn Abi Talib (s)) put up with all the instances of breaching of the covenants, and did not even object to those later when he was in power, fearing dispersion in the religion and turmoil in the ties which held the Muslims together. This was because the ideas of the Age of Ignorance were still in their minds and the hypocrites were on the watch to get a chance to create havoc. Now I do not know what is going to happen to me and you. Indeed there is no arbitrator but God. He is the only One who clarifies the truth. He is the best Separator.”
The following report contradicts it.
حدثنا علي بن أحمد بن محمد بن عمران الدقاق رضي الله عنه قال: حدثنا محمد بن أبي عبد الله الكوفي عن محمد بن إسماعيل البرمكي عن محمد بن عرفة قال: قلت للرضا عليه السلام يا بن رسول الله ما حملك على الدخول في ولاية العهد؟ فقال: ما حمل جدي أمير المؤمنين عليه السلام على الدخول في الشورى
Ali ibn Ahmad ibn Muhammad ibn Imran al-Daqqaq – may God be pleased with him – narrated that Muhammad ibn Abi Abdullah al-Kufi quoted on the authority of Muhammad ibn Isma’il al-Barmaki, on the authority of Muhammad ibn Arafat that he asked Al-Reza (s), “O son of the Prophet of God! What forced you to accept the succession to the throne?” The Imam (s) replied, “The same thing which forced my grandfather the Commander of the Faithful (s) to join the arbItraion council.”
Uyoon Akhbar al-Reza, by Shaykh Sadooq
Now if Imam Reza was definitely forced, to accept the successorship, why was he saying to the public that Mamun did this with good intentions and for the sake of Allah, and that he protected the ahlel bayt and gave them peace? Wasn’t he misguiding the people as well with these words, because when people would hear these words coming from the mouth of Imam Reza, they would definitely consider Mamun to be on the right path!
And the following report shows that Imam Reza didn’t want to be the successor because he considered himself incapable for the caliphate.
حدثنا أبو محمد الحسن بن يحيى العلوي الحسيني رضي الله عنه بمدينة السلام قال: أخبرني جدي يحيى الحسن بن جعفر بن عبيد الله بن الحسين قال حدثني موسى بن سلمة قال كنت بخراسان مع محمد بن جعفر، فسمعت أن ذا الرياستين الفضل بن سهل خرج ذات يوم وهو يقول: واعجبا لقد رأيت عجبا سلوني ما رأيت؟ فقالوا: ما رأيت أصلحك الله؟ قال: رأيت أمير المؤمنين يقول: لعلي بن موسى الرضا قد رأيت أن أقلدك أمر المسلمين وأفسخ ما في رقبتي وأجعله في رقبتك ورأيت علي بن موسى يقول له: الله الله لا طاقة لي بذلك ولا قوة فما رأيت خلافة قط كانت أضيع منها أمير المؤمنين يتفصى فيها ويعرضها على علي بن موسى وعلي بن موسى يرفضها ويأبى.
Abu Muhammad Al-Hassan ibn Yahya al-Alawi Al-Husseini – may God be pleased with him – narrated in Medina that his grandfather Yahya ibn Al-Hassan ibn Ja’far ibn Ubaydillah ibn Al-Hussein quoted on the authority of Musa ibn Salamat, “I was in the province of Khorasan with Muhammad ibn Ja’far. Then I heard that one day Thul-Riasatayn Al-Fadhl ibn Sahl came out and said, ‘I have dreamt something amazing. Ask me what I saw.’ They asked, ‘May God maintain your health! What did you dream?’ He said, ‘I dreamt that the Commander of the Faithful tell Ali ibn Musa Al-Reza (s), ‘I am planning to turn over the affairs of the Muslims to you, dismiss myself from the post of the Caliphate and put it on your shoulders.’ I saw that Ali ibn Musa (s) replied, ‘By God! I do not have the power to do this, nor do I have the strength.’ Fadhl added, ‘I had never seen the Caliphate more belittled than that. The Commander of the Faithful resigns and hands it over to Ali ibn Musa (s) , and Ali ibn Musa (s) turns him down and rejects it.’
Uyoon Akhbar al-Reza, by Shaykh Sadooq
Is Fadhl ibn Sahl mentioning a mere dream? The answer is , No. There is nothing like that in the Arabic text. The English translator added it himself, to show that this is the dream of Fadhl ibn Sahl. But the case is that , Fadhl ibn Sahl is narrating the incident which he saw. And nothing supports the idea that it is a dream.
So now, three different reports show three different pictures.
1. Imam Reza is happy with being made a successor.
2. Imam Reza is made a successor against his will.
3. Imam Reza doesn’t want to be made a successor because he considers himself incapable.