Sahih Bukhari Volume 009, Book 092, Hadith Number 400.
Hadith Section/Book: Sahih Bukhari Sahih Bukhari Book 92. Holding Fast to the Qur'an and Sunnah
Narrated By Ibn Masud : I was with the Prophet at one of the farms of Medina while he was leaning on a date palm leaf-stalk. He passed by a group of Jews and some of them said to the other, Ask him (the Prophet) about the spirit. Some others said, "Do not ask him, lest he should tell you what you dislike" But they went up to him and said, "O Abal Qasim! Inform us about the spirit." The Prophet stood up for a while, waiting. I realized that he was being Divinely Inspired, so I kept away from him till the inspiration was over. Then the Prophet said, "(O Muhammad) they ask you regarding the spirit, Say: The spirit its knowledge is with my Lord (i.e., nobody has its knowledge except Allah)" (17.85) (This is a miracle of the Qur'an that all the scientists up till now do not know about the spirit, i.e., how life comes to a body and how it goes away at its death.) (See Hadith No. 245, Vol. 6)