Ahmad b. Ali Ansaari narrates that Abu Salt al-Harawi said – One day Mamun told Imam Ali Reza (a.s.) – O Abul Hasan Reza (a.s.) tell me, why is it that your grandfather Ali – Ameerul Momineen (a.s.) became the one to divide Paradise and Hell. What is meant by this? I have thought a lot about this. Then Imam Ali Reza (a.s.) informed him – O Ameerul Momineen (i.e.
Mamun)! Has it not been narrated by your father, on the authority of your forefathers, on the
authority of Abdullah b. Abbas who said that he heard Allah’s Prophet (s) – Love for
Ali is faith, and despising him is atheism. Mamun said – Yes. Then Imam Ali Reza (a.s.) added – Therefore he is the one who divides Paradise and Hell as it is loving him which equals faith, and despising him which equals atheism. Then Mamun said – O Abul Hasan (Imam Reza (a.s.))! May Allah not let me live after you! I testify that you are the inheritor of the knowledge of Allah’s Prophet (s.a.w.a.)…
Oyoon Akhbaar al-Reza (a.s.) chap 32 trad 30