While I was asleep I saw (in a dream) a cup containing milk being presented to me. I took out of that until I perceived freshness being reflected through my nails. Then I presented the leftover to 'Umar b. Khattab. They said: Messenger of Allah: How do you interpret it? He said: This implies knowledge. (Using translation from Muslim 2391a)   

عَنْ رَسُولِ اللهِ ﷺ قَالَ بَيْنَا أَنَا نَائِمٌ إِذْ رَأَيْتُ قَدَحًا أُتِيتُ بِهِ فِيهِ لَبَنٌ فَشَرِبْتُ مِنْهُ حَتَّى أَنِّي لَأَرَى الرِّيَّ يَجْرِي فِي أَظْفَارِي ثُمَّ أَعْطَيْتُ فَضْلِي عُمَرَ بْنَ الْخَطَّابِ قَالُوا فَمَا أَوَّلْتَ يَا رَسُولَ اللهِ؟ قَالَ الْعِلْمُ