Bukhari Collection: ::Book Number 9:: Hadith # 157
Narrated `Abdullah bin `Umar:I heard Allah's Apostle saying, "While I was sleeping, I saw that a cup full of milk was brought to me and I drank of it and gave the remaining of it to `Umar bin Al-Khattab." They asked. What have you interpreted (about the dream)? O Allah's Apostle?" The Prophet said. "(It is Religious) knowledge."