Sayyiduna Hakim bin Hizam (may Allah be pleased with him) said: "The Messenger of Allah (peace and blessings be upon him) forbade me from four things in buying and selling: combining a loan with a sale, two conditions in one sale, selling what you do not have, and profiting from what you have not taken liability for."
Hadith Referenceالمعجم الكبير للطبراني / باب الحاء / 3133