Imam Sadiq (A.S.) said, "one day myself and my father came out of the assembly of Hasham. We happened to pass by a place where a group of Christians had come to ask questions from their scholar. We too went there to see what was the affair. We saw an old man with gray hair and gray eyebrows sitting among them. We also sat among the aggregation. The followers of Jesus Christ were sitting before him like worthless children, and were asking him questions. The old man's eye caught the sight of my father Imam Mohammad Baqir (A.S.) and he said, "Are you from among us or from among the followers of Mohammad (P.B.U.H.)."
My father answered from among the followers of Mohammad (P.B.U.H.). He said, "Are you from among the scholars or the ignorant"? My father said, "I am not from among the ignorant." The old man said, "Shall I ask you question or you will ask me." My father said, "You question me."
The aged man was surprised. He had a look upon my father and said, "Oh servant of God, let me know about the time which is neither day nor night."
My father replied, "Between the dawn and the sunrise."
He asked, "From which time is it?"
My father said, "From the times (hours) of the Paradise and the ailing ones gain their senses in this hour (time) and the pains become relieved and that one who had sleepless night goes to sleep at this time.
The man said, "The people in paradise eat and drink but do not excrete anything is there any thing in the world similar to them?"
My father said, "Yes the embryo which eats in the mother womb but nothing segregates from whatever it eats."
The man said, "Let me know if there is anything in the world similar to your claim that the people in paradise eat and drink but nothing is lessened and shortened and that returns to its original shape."
My father said, "Yes it is candle that if a hundred other candles are lit by it nothing gets lessened out of it."
The Christian scholar got up from his place and said, "This man is wiser then me." When he knew that he was Imam Mohammad Baqir (A.S.) he embraced Islam.
source : www.tebyan.net