Sahih Muslim
The Book of Transactions (Kitab Al-Buyu)
Book Number: 010 / Hadith Number: 3646
Ibn Umar (Allah be pleased with them) reported Allah's Messenger (may peace be upon him) as saying: He who buys foodgrain should not sell that before taking possession of it. He (the narrator) said: We used to buy foodgrain 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.