From Sahih Bukhari (Hadith 7032):
Narrated `Abdullah bin `Umar:I heard Allah's Messenger (ﷺ) 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 Messenger (ﷺ)?" The Prophet (ﷺ) said. "(It is Religious) knowledge
Reference: Bukhari 7032