Waqqas, 'Abd al-Rahman ibn al-Aswad ibn 'Abd Yaghuth (1), Ibn Mu'ayqib al-Dawsi (2), al-Hakam, Hammad, Malik, and al-Layth; due to what was narrated from Ma'mar ibn 'Abd Allah, that he sent his servant with a sa' of wheat and said: "Sell it, then buy barley with it." The servant went and took a sa' and an extra [fraction] of a sa'. When he came to Ma'mar, he informed him of that. Ma'mar said to him: "Why did you do that? Go and return it, and do not take anything but like for like, for the Prophet, peace and blessings be upon him, forbade the sale of food for food unless it is like for like, and our food on that day was barley." It was said: "But it is not the same as it." He replied: "I fear it may be analogous (3)." Related by Muslim (4). And because one of them is adulterated with the other, they are like two types of the same genus. Our position is the statement of the Prophet, peace and blessings be upon him: "Sell wheat for barley as you wish, hand to hand" (5). In another wording: "There is no harm in selling wheat for barley, even if the barley is the greater of the two, hand to hand, but as for on credit, then no" (6), and in another wording: "If these types differ, then sell as you wish" (6). This is explicit and authentic, and it is not permissible to abandon it without an equivalent counter-argument. Also, they do not share a specific name, so they are not one genus, just like dates and wheat. Furthermore, they are named in the Six Species, so they are two genera, like the rest of them. The hadith of Ma'mar must necessarily imply [the concept of] genus, by analogy with the rest of the genera of food; it is also possible that he meant the food commonly known to them, which was barley, for he said in the report: "And our food on that day was barley." Then, even if it were...