Parashas Metzora · Passuk 15:28
Chabad.org — English translation + Rashi
Torah Temima points to Toras Kohanim.
English: “And afterward she shall be pure” — “afterward” after all of them — that impurity not interrupt between them.
Consecutive clean days
Chazal require the seven clean days to be consecutive without a new sighting interrupting the count.