The second is that their impurity is known. If their impurity is known, they must not be used until they are washed. If their purity is known, then there is no difficulty. The question, however, concerns the case in which their condition is unknown: should we say that the basic assumption is that they do not guard themselves against impurities, even though such impurities are forbidden, or should we say that the basic assumption is purity until their impurity becomes evident? The latter is the answer.

The hide of a carcass is not purified by tanning …

His statement, “The hide of a carcass is not purified by tanning”: tanning is the removal of the filth and foul matter present in the hide by means of substances added to water.

Thus, when the hide of a carcass is tanned, the author maintains that it does not become pure through tanning.

If it is asked: Does the hide of a carcass become impure?

The answer is: if the carcass itself is pure, then its hide is pure; but if it is impure, then its hide is impure.

An example of a pure carcass is fish, due to Allah’s saying: “Lawful to you is the catch of the sea and its food” [al-Ma'idah 5:96].

Ibn Abbas, may Allah be pleased with him and his father, said: “Its catch is that which is taken alive, and its food is that which is taken dead” (1).

Its hide is therefore pure.

As for that which becomes impure upon death, its hide becomes impure upon death, due to Allah’s saying: “unless it be carrion, spilled blood, or the flesh of swine—for indeed it is”