TT #166 · Parshas Tazria · Aliyah 3 · Passuk 23
English: If the bright spot remains in its place and has not spread, it is the scar of the boil, and the priest shall pronounce him clean.
Chabad.org — Chumash, English translation + Rashi for Vayikra 13:23
Torah Temimah cites Sifra (Toras Kohanim) for the recognizable crusted stage of the scar of a boil.
Sifra — Vayikra 13, Midrash Sefer
English: The scar of the boil has formed when it crusts like the peel of a garlic clove.
Textual derivation
The scar is identified by a crust comparable to the peel of a garlic clove, rather than an actively open lesion.