Mu’ammar bin ‘Abdullah narrates that he sent his slave with one sa’ of wheat and said:“Sell this one sa’ and bring back whatever you buy with it.”The slave went and received one sa’ and a little more in exchange. When he returned and informed him about it, Mu’ammar said:“Why did you do that? Go and return it, and only make an equal exchange, for I heard the Prophet (peace and blessings be upon him) say: ‘Grain for grain.’”He meant that only equal amounts can be given and taken. In those days, this was our food. The slave said:“But these are not the same.”Mu’ammar replied:“I fear that they are equivalent.”