Sayyiduna Abdullah bin Abbas (may Allah be pleased with them both) said that the Messenger of Allah (peace and blessings be upon him) said: "Whoever buys foodstuff should not sell it until he has measured it." I said to Ibn Abbas (may Allah be pleased with them both): Why? He said: Do you not see that they trade gold among themselves while the foodstuff is still lying there?
Hadith Referenceالسنن الكبرى للبيهقي / كتاب البيوع / 10686
Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) said that the Messenger of Allah (peace and blessings be upon him) "forbade anyone to sell foodstuff that he bought by measure before taking possession of it."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب البيوع / 10688