Qassim bin Abdurrahman

Al-Qassim bin Abdurrahman, who was a Zaydite, said, ‘One day, I went to Baghdad. I saw people look forward and stop in crowds. I asked what that was and it was said to me that it was the son of ar-Redha. I said to myself, ‘By Allah, I must see him.’ He came riding on a mule. I cursed (with myself) those who believed in imamate where they said that Allah had made it obligatory to obey this man.
Imam al-Jawad looked at me, came towards me and said, ‘O Qassim bin Abdurrahman, (Is it a mortal man, alone among us, that we are to follow? Then indeed we should fall into error and madness). I was astonished when he knew my intention and then I turned to believe in his imamate.’ ( Ithbat al-Hudat, vol.6 p.19 )

Reference : The Life of Imam Muhammad Al-Jawad