Sahih Bukhari, Chapter: Sales and Trade

Ibn Umar told us that the people used to buy food from the caravans in the lifetime of the Prophet. The Prophet used to forbid them to sell it at the very place where they had purchased it (but they were to wait) till they carried it to the market where foodstuff was sold. Ibn Umar said, 'The Prophet also forbade the reselling of foodstuff by somebody who had bought it unless he had received it with exact full measure'