It is narrated about Mu’ammar bin ‘Abdullah that he sent his slave with a sa’ of wheat and said:“Sell it for a sa’ and bring back whatever you buy with it.”The slave went and received a sa’ and a little more than a sa’. When he returned and informed him about it, Mu’ammar said:“Why did you interfere in this? Go and return it, and only make an equal exchange, because I heard the Prophet (peace and blessings of Allah be upon him) say: Grain for grain can only be exchanged equally.”The narrator says: In those days, our food used to be barley. It was said to Mu’ammar: This is not like it. So he replied:“I think it is like it.”