Mamar binAbdullah reported that he sent his slave with a sa of wheat and said to him: Sell it, and then buy with it barley. The slave went away and he got a sa (of barley) and a part of sa over and above that. When he came to Mamar he informed him about that, whereupon Mamar said to him: Why did you do that? Go back and return that, and do not accept but weight, for weight, for I used to hear from Allahs Apostle ﷺ as saying: Wheat for wheat and like for like. He (one of the narrators) said: Our food in those days consisted of barley. It was said to him (Mamar) that (wheat) is not like that (barley). He replied: I am afraid these may not be similar