TT #202 · Parshas Tazria · Aliyah 5 · Passuk 31
English: If the priest examines the netek and its appearance is not deeper than the skin, and there is no black hair in it, he shall isolate the netek for seven days.
Chabad.org — Chumash, English translation + Rashi for Vayikra 13:31
Torah Temimah cites Sifra (Toras Kohanim) for the exemption that follows when qualifying hair is present.
Sifra — Vayikra 13, Midrash Sefer
English: If the required hair is present, the person is exempt from the impurity ruling.
Textual derivation
The presence of qualifying hair prevents the stated impurity.