369.Narrated Abdullah (Allah be pleased with him): While I was going with the Prophet (peace be upon him) through the ruins of Medina and he was reclining on a date-palm leaf stalk, some Jews passed by. Some of them said to the others; Ask him (the Prophet (peace be upon him)) about the spirit. Some of them said that they should not ask him that question as he might give a reply, which would displease them. But some of them insisted on asking, and so on of them stood up and asked, "O Aba-l-Qasim! What is the spirit?" The Prophet (peace be upon him) remained quiet. I thought he was being inspired Divinely. So I stayed till that state of the Prophet (while being inspired) was over. The Prophet (peace be upon him) then said, "And they ask you (O Muhammad (peace be upon him) ) concerning the spirit - Say: The spirit - its knowledge is with my Lord. And of knowledge you have been given but little." (17:85).
(Sahih Al-Bukhari Vol 1).
(Dr. Muhammad Muhsin Khan et.al.).