TT #259 · Parshas Tazria · Aliyah 7 · Passuk 47
English: If a garment has a lesion of tzaraas, whether in a wool garment or a linen garment,
Torah Temimah cites Sifra (Toras Kohanim) for requiring wool to retain its natural form.
Sifra — Vayikra 13, Midrash Sefer
English: The Sifra derives that, just as linen retains its natural form, the wool must likewise remain in its natural form.
Textual derivation
The wool must retain its natural character, just as the linen does.