This article was taken from seratonline.com
Masoodi – the reputed historian – records on the authority of Himyari that the slave of Imam Jafar Ibn Muhammad (a.s.), Muhammad Ibn Saeed, reports that after the martyrdom of Imam Muhammad Taqi (a.s.), Umar Ibn Faraj al-Rukkhaji (may Allah curse him) came to Medina from Hajj. (It should be noted that this Umar was the real brother of Muhammad Ibn Faraj who was a great Shiite scholar and companion of the Imams (a.s.). Indeed Allah guides whosoever He wishes).
Umar collected the enemies of the Ahle Bait (a.s.) from the people of Medina and instructed, ‘Guide me to an enemy of the Ahle Bait (a.s.) who is an expert in Quranic sciences, Arabic literature and other sciences so that I can hand over this child (Imam Ali Naqi a.s.) to him in order to teach him and prevent the Rafizis from meeting him.
They introduced him to Abu Abdillah Junaidi, an expert in the aforementioned sciences, who was notorious for his enmity and hatred towards the Ahle Bait (a.s.). Umar invited him, conferred him with worldly bounties and said, ‘The Emperor has ordered you to educate this child and not to allow his Shias to meet him.’
Junaidi agreed and imprisoned Imam Ali Naqi (a.s.). He appointed a man from Basra to monitor Imam (a.s.) but kept the key of the place only with himself. Imam (a.s.) was in his captivity for a considerable period of time. Thus, it was almost impossible for the Shias to frequent Imam (a.s.) and ask him their queries.
One Friday, I (Muhammad Ibn Saeed), met Junaidi, greeted him and asked him, ‘How is that Hashemi boy?’ He frowned and retorted, ‘You call him a boy? You should call him an old Hashemi man. You know that there’s none in Medina more learned than me. But by Allah! When I pose the most difficult of questions in Arabic literature to him (a.s.) thinking that I will stump him with my queries, he starts answering in such a way that I start learning many things from him. People are under the impression that I am teaching him but the fact is the other way round.’ Hearing this, I just departed from him as I have not heard anything.
After a few days, I met him again and asked, ‘How is that Hashemi youth?’ He responded, ‘Please don’t ask me about him. By Allah! He is the best inhabitant of earth and the most superior of Allah’s creatures. When he (a.s.) expresses his desire of going home, I tell him to learn some chapter of the Holy Quran. He asks, ‘Which chapter?’ I mention a very lengthy chapter where he has not even reached. But he starts reciting it in such a beautiful voice – similar to that of Prophet Dawood (a.s.) – that I have never heard anybody reciting in a sweeter voice. When his father died in Iraq, he was a child. Thereafter, he was put in the company of black slave girls. Hence, I am stunned from where he has learnt all these things.’
After a few days, when I met Junaidi, I realized that he had become a Shia and believed in the divine Imamate of Imam Ali Naqi (a.s.).
Ithbaat al-Wasiyyah p. 230-231