Midrash su Levitico 13:59

12) (Vayikra 13:59) ("This is the law of the plague-spot of leprosy, in a garment of wool or linen, or in the warp, or in the woof, or in any article of skin, to declare it clean or to declare it unclean.") "This is the plague-spot of leprosy, etc.": (Vayikra 14:54) ("This is the law for all plague-spots or leprosy and for a nethek (Vayikra 14:55) and for the leprosy of a garment and of a house.") They (plague-spot garments) are being likened to a house, viz., Just as a house is rendered unclean by the entry (of an unclean person), so it is rendered unclean by the entry of all (plague-spot garments). — But perhaps just as a house requires birds (for its cleansing, [viz. Vayikra 14:49]), so all (plague-spot garments) should require birds (for their cleansing)! It is, therefore, written "This" (i.e., only in this respect [that of "entry"] are they similar, and not in the other.) Rebbi says: It is written "This is the law for all plague-spots of leprosy and for a nethek and for the leprosy of a garment and of a house." Just as a house renders unclean by entry, so all are rendered unclean by entry. This tells me only of a garment. Whence do I derive all of them (i.e., warp and woof, etc.) for inclusion? From "This is the law of the plague-spot of leprosy … in the warp or in the woof, etc." Just as a garment renders unclean by entry, so all (i.e., warp and woof, etc.) render unclean by entry. — But perhaps just as a garment is rendered unclean by all that are tamei (e.g., sheratzim, semen, etc.), so all (warp and woof etc.) are rendered unclean by all that are tamei! It is, therefore, written "This" (and not the others).

13) "to render it clean and to render it unclean": Just as it (the law of plague-spots) is a mitzvah in Eretz Yisrael, so it is a mitzvah outside Eretz Yisrael. "to declare it clean or to declare it unclean": Just as it is a mitzvah to declare it clean, so it is a mitzvah to declare it unclean. "to declare it clean or to declare it unclean": The Cohein who declares it clean declares it unclean, and if he dies, a different Cohein inspects it.