Sayyiduna Abu al-Tufayl (may Allah be pleased with him) narrates: The Prophet (peace and blessings be upon him) said: "Last night (in a dream) I was drawing water when black and greyish sheep came to me. Then Abu Bakr came and drew one or two buckets, and there was weakness in his drawing; may Allah Almighty forgive him. Then Umar came, and it became a huge bucket; he filled the troughs and gave water to all who came. I have not seen anyone as diligent as Umar at drawing water. I interpreted this to mean that the black sheep are the Arabs and the greyish sheep are the non-Arabs ('Ajam)."
Imam al-Tabarani recorded it, and its chain is hasan (good).
Hadith Referenceمجمع الزوائد ومنبع الفوائد / كتاب المناقب / 14447