For example, if he wears two leather socks, one of them torn on top and the other torn underneath, then the foot is presently covered; but if either one were worn alone, wiping over it would not be permissible. Therefore, wiping over both of them is not permissible.
If both are intact, however, wiping over both of them is permissible, because if either one were worn alone, wiping over it would be permissible.
The correct view is that wiping over both of them is permissible without restriction, based on the view that covering the area required to be washed is not a condition, so long as the item still retains the designation of a leather sock.
If one wears a leather sock over another in a manner in which wiping is valid, then if this is done before invalidating his ablution, the ruling applies to the upper one; but if it is done after invalidating his ablution, the ruling applies to the lower one. Thus, if he puts on a leather sock, then invalidates his ablution, and then puts on another leather sock, the ruling applies to the lower one, and it is not permissible for him to wipe over the upper one.
If he puts on the upper one after invalidating his ablution and wipes over the lower one, the ruling applies to the lower one. This is like one who puts on a leather sock, then invalidates his ablution, then wipes over it, and thereafter puts another leather sock over the first while he is in a state of purity attained through wiping when he puts on the second one. The established position of the school is that the ruling applies to the lower one, because he put on the second one after invalidating his ablution.
Some scholars said: If he puts on the second one while in a state of purity, he may wipe over it (1), because it is true of him that he put his feet into them while pure. The Prophet, may Allah’s peace and blessings be upon him, said: “For I put them on while they were pure” (2). This includes purity attained through washing as well as through wiping, and this is a strong view, as you can see. It is further supported by the fact that the scholars of the school expressly stated that wiping over the two leather socks removes the state of ritual impurity. Thus, he put on the second one in a complete state of purity, so why should he not wipe over it? (3).