Musannaf Ibn Abi Shayba 13:3154

Abu Bakr narrated to us, he said: Muhammad ibn Abi ‘Adi narrated to us, from Ibn ‘Awn, who said: A man hired himself out for a year for one thousand dirhams. He said: So he said to me, "Ask Muhammad, for they have paid me in advance." So I asked him, and he said, "I see no harm in it."