Sahih Muslim Book 39, Hadith Number 6712.
‘Abdullah(b. Mas’ud) reported: As I was going along with Allah’s Apostle (may peace be upon him) in a cultivable land and he (the Holy Prophet) was walking with the support of a wood, a group of Jews happened to meet him. Some of them said to the others: Ask him about the Soul. They said: What is your doubt about it? There is a possibility that you may ask him about anything (the answer of) which you may not like. They said: Ask him. So one amongst them asked him about the Soul. Allah’s Messenger (may peace be upon him) kept quiet and he gave no reply and I came to know that revelation was being sent to him, so I stood at my place and thus this revelation descended upon him: “They ask thee ‘about Soul. Say: The Soul is by the Commandment of my Lord, and of Knowledge you are given but a little” (xvii. 58).