Musnad Abu Ya'la al-Mawsili 247:11

Abu Bakr narrated to us, Ahmad ibn Abdullah narrated to us, he said: Umm al-Aswad narrated to me, from Munyah, from the hadith of Abu Barzah, he said: The Prophet, peace and blessings of Allah be upon him, had nine wives. One day he said: "The best of you is the one with the longest hand." So each one of them stood up and placed her hand against the wall. He said: "I do not mean this, but rather the one who is most generous with her hands."