TT #111 · Parshas Tazria · Aliyah 2 · Passuk 10
English: The kohen shall look [at it]. And, behold! there is a white se'eith on the skin, and either it has turned the hair white, or there is healthy, live flesh in the se'eith.
Chabad.org — Chumash, English translation + Rashi for Vayikra 13:10
Torah Temimah cites Sifra (Toras Kohanim) for the minimum size of a healthy-flesh patch, measured by the two-hair standard.
Sifra — Vayikra 13, Midrash Sefer
English: Healthy flesh must occupy an area corresponding to two hairs.
Textual derivation
The healthy-flesh patch must be at least the area of two hairs, using the same minimum measure as the white-hair sign.