Sahih Muslim Book 10, Hadith Number 3646.

Chapter : It is invalid to sell the commodity before taking possession of it.

Ibn Umar (Allah be pleased with them) reported Allah’s Messenger (may peace be upon him) as saying: He who buys food-grain should not sell that before taking possession of it. He (the narrator) said: We used to buy food-grain from the caravans in bulk, but Allah’s Messenger (may peace be upon him) forbade us to re-sell that until we had shifted it to some other place.