is one genus according to all narrations, because the name 'cattle' encompasses them both. This is not correct, because their meat is two genera, so their milk is two genera, like camels and cattle. It is permissible to sell milk for a non-genus with a surplus (tafadul), in whatever manner one wishes, hand-to-hand, and for its own genus as equivalents by measure. Al-Qadi said: It is a measured item (makil) and is only sold by measure, because that is the custom regarding it. There is no difference between them both being fresh, both being sour, or one being fresh and the other sour, because changing the quality does not prevent the permissibility of the sale, just like quality and inferiority. If one of them is mixed with water or otherwise, it is not permissible to sell it for pure milk or for mixed milk of its own genus, because it contains something of a non-genus for a reason other than its benefit.

Section: Two categories branch off from milk: that which contains nothing else, such as butter, clarified butter (samn), buttermilk (makhid), and colostrum (liba'). And that which contains something else. Both are not permitted to be sold for milk, because they are derived from milk, so it is not permissible to sell them for their origin from which they are derived, like an animal for its meat, or sesame for its oil (shairaj). This is the school of al-Shafi'i. From Ahmad, there is a view that it is permissible to sell milk for butter if the standalone butter is more than the butter contained in the milk. This implies the permissibility of selling it for a surplus, and the prohibition of its permissibility as equals. Al-Qadi said: This narration does not follow from the school (Madhab), because when two things are subject to riba, it is not permissible to sell one for the other while it contains something of a non-genus, like a mudd of 'ajwa dates and a dirham for two mudds. The correct view is that this narration indicates the permissibility of the sale in the issue of the mudd of 'ajwa, and its being contrary to other narrations does not prevent it from being a narration, like all other narrations that contradict others, but it is contrary to the apparent position of the school. The ruling on clarified butter (samn) is the same as the ruling on butter. As for milk for buttermilk that contains its butter, it is not permissible. Ahmad explicitly stated this, saying: There is no good in milk for buttermilk. The permissibility can be inferred similarly to the one before it.