Pour a bucket of water over his urine.' The command implies obligation, and because it is an impure place, it is not purified except by washing, just like clothes. As for the hadith of Ibn Umar, it was reported by al-Bukhari, and it does not contain the mention of urine. It is possible that he meant they used to urinate, then come and go in the mosque, so their coming and going was within it after their urination.

Section: Impurity is not purified by transformation (istihala). If impure manure (sirjin) is burned and becomes ashes, or if a dog falls into a salt pan and becomes salt, it does not become pure, because it is an impurity that did not occur through transformation, and thus it is not purified by it, just like blood when it becomes pus or sanies. Wine has been cited as a corollary; it is impure by transformation, so it is possible that it could be purified by it.

Section: Water separated from the washing of an impurity is divided into three categories: The first is that it separates while changed by it; it is impure by consensus, because it has been changed by the impurity, so it is impure, just as if it had been poured onto it. The second is that it separates unchanged before the place is purified; it is also impure, because it is a small quantity of water that has encountered an impurity without purifying it, so it is impure, like that which has been changed, and like the remainder [of the water] in the place; for that which remains in the place is impure, and it is a part of the water with which the impurity was washed, and because it was impure while in the place, and squeezing it out does not make it pure.

The third: Water that separates unchanged from the washing that has purified the place; there are two views regarding it, the most correct of which is that it is pure. This is the view of al-Shafi'i, because it is a part of the connected [water], and the connected [water] is pure, so the separated [water] is likewise. Furthermore, it is water that has removed the ruling of the impurity without having been changed by it, so it is pure, like that which separates from the earth. The second view is that it is impure, which is the view of Abu Hanifa, because it is a small quantity of water that has encountered an impurity and was thereby made impure, just as if it had been poured onto it. If we judge it to be pure, is it then a purifying agent (tahur)? There are two views: one is that it is a purifying agent, because its original state is purity, and what occurred to it did not make it impure, nor did it change it, so its status as a purifying agent was not lost, just as if one had washed a pure garment with it. The second is that it is not a purifying agent, because it removed an impediment to prayer, similar to that by which ritual impurity (hadath) is removed.