Musnad Ahmad 30:2692

Yazid narrated to us, Muhammad informed us, from Abu Salamah, from Abu Hurairah, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "While I was at a well drawing water, Abu Bakr came and drew a bucket or two, and there was weakness in his drawing, and may Allah forgive him. Then Umar came and drew until it transformed in his hand into a large bucket, and the people watered their camels until they were satisfied, and I have never seen a genius (abqari) performing his feat like him."