Sahih Bukhari Volume 001, Book 003, Hadith Number 082.
Narated By Ibn 'Umar : Allah's Apostle said, "While I was sleeping, I saw that a cup full of milk was brought to me and I drank my fill till I noticed (the milk) its wetness coming out of my nails. Then I gave the remaining milk to 'Umar Ibn Al-Khattab" The companions of the Prophet asked, "What have you interpreted (about this dream)? "O Allah's Apostle ,!" he replied, "(It is religious) knowledge."