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 ﷺ said. "(It is Religious) knowledge."

حَدَّثَنَا قُتَيْبَةُ بْنُ سَعِيدٍ، حَدَّثَنَا اللَّيْثُ، عَنْ عُقَيْلٍ، عَنِ ابْنِ شِهَابٍ، عَنْ حَمْزَةَ بْنِ عَبْدِ اللَّهِ، عَنْ عَبْدِ اللَّهِ بْنِ عُمَرَ ـ رضى الله عنهما ـ قَالَ سَمِعْتُ رَسُولَ اللَّهِ ﷺ يَقُولُ " بَيْنَا أَنَا نَائِمٌ أُتِيتُ بِقَدَحِ لَبَنٍ فَشَرِبْتُ مِنْهُ، ثُمَّ أَعْطَيْتُ فَضْلِي عُمَرَ بْنَ الْخَطَّابِ ". قَالُوا فَمَا أَوَّلْتَهُ يَا رَسُولَ اللَّهِ قَالَ " الْعِلْمَ ".