Musnad Ahmad 1099:10

'Abd al-Samad narrated to us, Hammad ibn Salamah narrated to us, 'Ali ibn Zayd narrated to us, from Abu al-Tufayl, who said: The Messenger of Allah (ﷺ) said: "I saw in what a sleeper sees as if I were drawing water from a well, and black sheep and dust-colored sheep came to me. Then Abu Bakr came and drew a bucket or two, and there was weakness in them, and may Allah forgive him. Then 'Umar came and drew, and it transformed into a large bucket, and he filled the trough and quenched the thirst of those who came to drink. I have not seen a genius who draws water better than 'Umar. I interpreted the black ones as the Arabs, and the dust-colored ones as the non-Arabs."