Sahih Bukhari Volume 9, Book 91, Hadith 7008

حَدَّثَنَا عَبْدَانُ، أَخْبَرَنَا عَبْدُ اللَّهِ، أَخْبَرَنَا يُونُسُ، عَنِ الزُّهْرِيِّ، أَخْبَرَنِي حَمْزَةُ بْنُ عَبْدِ اللَّهِ، أَنَّ ابْنَ عُمَرَ، قَالَ سَمِعْتُ رَسُولَ اللَّهِ صلى الله عليه وسلم يَقُولُ ‏"‏ بَيْنَا أَنَا نَائِمٌ أُتِيتُ بِقَدَحِ لَبَنٍ، فَشَرِبْتُ مِنْهُ، حَتَّى إِنِّي لأَرَى الرِّيَّ يَخْرُجُ مِنْ أَظْفَارِي، ثُمَّ أَعْطَيْتُ فَضْلِي ‏"‏‏.‏ يَعْنِي عُمَرَ‏.‏ قَالُوا فَمَا أَوَّلْتَهُ يَا رَسُولَ اللَّهِ قَالَ ‏"‏ الْعِلْمَ ‏"‏‏

Narrated By Ibn 'Umar : I heard Allah's Apostle saying, "While I was sleeping, I was given a bowl full of milk (in a dream), and I drank of it to my fill until I noticed its wetness coming out of my nails, and then I gave the rest of it to 'Umar." They (the people) asked, "What have you interpreted (about the dream)? O Allah's Apostle?" He said, "(It is Religious) knowledge."