During the time Imam Hasan Askari (a.s) was in imprisonment at Baghdad, for three years at a stretch there was a severe famine. A Christian scholar arrived there and showing a miracle of causing rain he created a great turmoil in the beliefs of Muslims. Everyone began to extol his spiritual feats and the truth of Christian faith. The news reached Motamid.
He summoned him and requested him to cause rain. Immediately he raised his hands to the sky and uttered a few words. Within no time a black cloud spread on the sky and it began to rain. Motamid also began to have faith in his miracle and the beliefs of all his courtiers became shaky. Motamid realized that the best course of action was to somehow send this Christian away from his court.
When he departed a debate began on this matter. No one could explain it away. A courtier said that except for Imam Hasan Askari (a.s) no one could solve this puzzle. It was ordered to bring him to the court at once.
It is mentioned in Sawaiqul Mohreqa that when Imam (a.s) arrived, Motamid related to him the whole incident. He said, “What is so great about it? People should accompany me outside the town and if Allah wills, I will clarify the whole matter. But the condition is that all prisoners must be released.” Thus it happened in this way. The Christian monk was also summoned. Imam said, “Now you invoke and show your miracle.
” He raised his hands and began to recite something inaudibly. At once, a cloud appeared. Imam (a.s) told a man next to him, “Catch hold both the hands of the monk and snatch whatever he is holding.” The man did as commanded and came to the Imam holding a bone. The Imam buried this bone in the soil and told the Christian, “Now let’s see if it rains or not.” Again he raised his hands, but leave alone rain, the cloud that had appeared also dispersed.
Imam (a.s) told Motamid, “There was no miracle in this man; it is in the bone that he was holding. It is a bone of some prophet that he somehow got. It is the specialty of this bone that when it is shown to the open sky, at once a cloud will appear and rain.” Hearing this, the doubts of the people were dispelled and the misplaced faiths again returned to their original position.
(Managhib, by Ibn–Shahr‘ashub, v.4, p.425)