Musannaf Ibn Abi Shayba 13:3124

Abu Bakr narrated to us, he said: Abu Mu'awiyah narrated to us, from Wa'il ibn Dawud, from Sa'id ibn 'Umayr, who said: The Prophet, peace and blessings of Allah be upon him, was asked: "Which earning is the purest?" He said: "A man's work with his own hand, and every righteous sale."