Shayban ibn Farrukh narrated to us, saying: Abd al-Warith narrated to us, from Ibn Abi Najih, who said: Abdullah ibn Kathir narrated to me, from Abu al-Minhal, from Ibn Abbas, who said: The Messenger of Allah, peace and blessings be upon him, arrived while the people were practicing salaf (advance payment for goods). The Messenger of Allah, peace and blessings be upon him, said to them: "Whoever makes a salaf transaction, let him not make it except with a known measure and a known weight."