Yusuf bin Mahak narrated from Hakim bin Hizam (may Allah be pleased with him), who said: I said: O Messenger of Allah! A man comes to me wanting to buy something from me that I do not have; should I buy it for him from the market? He (peace and blessings be upon him) said: "Do not sell what you do not have."
Hadith Referenceالمعجم الكبير للطبراني / باب الحاء / 3085