It is narrated from Sayyiduna Ibn Umar (may Allah be pleased with them both) that the Messenger of Allah (peace and blessings be upon him) said: Whoever buys grain should not sell it until he has taken possession of it. And we used to buy grain in heaps from the riders, then the Messenger of Allah (peace and blessings be upon him) forbade us from selling that heap before moving it from its place.