al-Ma`arij 70:4; an-Naba' 78:38; al-Qadr 97:4
The hadith say this about its circumstances :
* Narrated 'Abdullah:Razi said that after this answer, the Jews said to Muhammad, 'is this answer (You have been given only a little [knowledge]) addressed to us alone or are you included with us? He said 'It is us and you who were given of a little knowledge.' (Razi, At-Tafsir Al-Kabir, commenting on Q. 17:85) In contrast to the followers of Mohammad who were, "given of knowledge nothing except a little," the people of the Book were called people "possessed of knowledge."
While I was going with the Prophet 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) 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 one of them stood up and asked, "O Aba-l-Qasim! What is the spirit?" The Prophet 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 then said, "And they ask you (O Muhammad) concerning the spirit --Say: The spirit -- its knowledge is with my Lord. And of knowledge you (mankind) have been given only a little)." (bani Isra'il 17:85) (Sahih Bukhari 1.127)