Parashas Metzora · Passuk 14:47
Chabad.org — English translation + Rashi
Torah Temima points to Toras Kohanim.
English: “He shall wash his garments” — every [other] washing of garments in the Torah is a stringency, but this is a leniency: even if he is wearing ten garments, all remain pure until he has stayed long enough to eat a peras.
Leniency of the time requirement
Chazal note that this particular garment-washing law is unusually lenient; brief presence does not render the clothes tamei.