Musannaf Ibn Abi Shayba 13:440

Abu Bakr narrated to us, he said: Waki’ narrated to us, from Abu al-Mutarrif, from his father, from his grandfather, from Shurayh: That he did not see any harm in him giving him a garment and saying, "Sell this garment for such and such, and whatever you increase [the price] by, it is yours."