Shaykh Tusi mentions in the Amali quoting from Mūsa Ibn Abdul Aziz that he said: One Christian Physician by the name of Yohanna came to me and said, ‘I put you under the oath of your religion and your Prophet, you tell me whether the man buried in Karbala, for whose Ziarat people come in hordes, was a companion of the Prophet?’ I said, ‘No! He was the grandson of our Prophet (S), Hazrat Husain (a.s.). Now! I put you under oath to tell why you had posed such a question to me?’ He said: I have heard a very strange tale about him. One night, Shapūr the servant of the accursed Caliph Harūn came to me and took me to Mūsa Ibn Isa a close relative of the Caliph.
I found him unconscious on his bed. His internal organs were lying in a pail before him. Those days Harūn had summoned him from Kufa. Shapūr asked the special servant of Mūsa what was the matter with his master. He said that he was all right a few hours ago and chatting with his colleagues. One of them was Hashemite. He was saying: I was seriously ill and all the doctors had failed to cure my sickness. My scribe suggested that I seek the cure from the Turbah of Hazrat Husain (a.s.). I followed this advice and was cured.
Mūsa asked him if he had a piece of that turbah remaining with him? ‘Yes’, he said, and sent someone to get it for Mūsa at once. In order to defile it Mūsa threw it in the drain pipe of his bathroom. Suddenly Mūsa screamed ‘Fire! Fire!’ as if he was burning in fire. He asked for a pail and what you see in it are the pieces of his internal organs. Seeing that, all his friends left his house and a state of mourning descended on his family.
Shapūr told me to remain there for the night and observe his condition and draw some conclusion. He stayed for the night and Mūsa expired at dawn.
The narrator says that Yohanna the Christian visited the tomb of Imam Husain (a.s.) many times and ultimately he accepted Islam and remained a Muslim all his life. This report is also mentioned in the 10th volume of Bihār al-Anwār.