Mukhtasar Bukhari

Narrated from Sayyiduna Ibn Umar (may Allah be pleased with them both) that during the time of the Prophet Muhammad (peace and blessings be upon him), people used to buy grain from caravan people. Then the Prophet Muhammad (peace and blessings be upon him) would send a man to them who would prohibit them from selling that grain at that very place until they had brought it to the place where grain is sold (i.e., the market). And Ibn Umar (may Allah be pleased with them both) also said that the Prophet Muhammad (peace and blessings be upon him) forbade selling grain or foodstuff at the same time it is purchased, without taking possession of it (and moving it to another place).