Sunan Abi Dawud — Wages (Kitab Al-Ijarah) — Hadith No: 3503
Translation
Narrated Hakim ibn Hizam: Hakim asked (the Prophet): Messenger of Allah, a man comes to me and wants me to sell him something which is not in my possession. Should I buy it for him from the market? He replied: Do not sell what you do not possess