Musnad Ahmad 180:7

Aswad ibn Amir narrated to us, he said: Sharik narrated to us, from Wa'il, from Jami' ibn Umayr, from his maternal uncle, who said: The Prophet, peace and blessings of Allah be upon him, was asked about the best of earnings, and he said: "A righteous sale, and a man's work with his own hand."