TT #101 · Parshas Tazria · Aliyah 2 · Passuk 6
English: And the kohen shall see him on the seventh day a second time. And, behold! the lesion has become dimmer, and the lesion has not spread on the skin, the kohen shall pronounce him clean. It is a mispachath. He shall immerse his garments and become clean.
Chabad.org — Chumash, English translation + Rashi for Vayikra 13:6
Torah Temimah cites Megillah 8b for the scope of purification after a skin affliction is declared healed.
E-Daf — Megillah 8b · Shas.org · Sefaria — Megillah 8b, source text and translation
English: The Gemara explains the verse “the priest shall pronounce him clean ... and he shall wash his clothes and be clean.” Its conclusion is that he is now pure from causing impurity through entering a house retroactively, even if he later develops a confirmed sign.
Textual derivation
The verse teaches that a person purified after quarantine does not retroactively impart impurity to a house he entered before the later confirmed sign appeared.