TT #152 · Parshas Tazria · Aliyah 3 · Passuk 18
English: When the flesh has a boil on its skin and it heals.
Chabad.org — Chumash, English translation + Rashi for Vayikra 13:18
Sifra (Toras Kohanim).
Sifra — Vayikra 13, Midrash Sefer
English: The boil must be healed enough that it is no longer active, but it need not have healed to the point of leaving a scar: it is in an intermediate state.
Textual derivation
The boil must be partly healed: no longer active, but not necessarily healed to the point of scarring.