TT #10 · Parshas Tazria · Aliyah 1 · Passuk 2
English: Speak to the Israelite people thus: When a woman at childbirth bears a male, she shall be impure seven days; she shall be impure as at the time of her condition of menstrual separation.
Chabad.org — Chumash, English translation + Rashi for Vayikra 12:2
Torah Temimah cites Sifra (Toras Kohanim).
Daat — Sifra (Toras Kohanim) on Vayikra 12
English: One might have thought that the seven days could be consecutive or scattered. Scripture says, “as in the days of the menstruation of her sickness she shall be impure”: just as her menstrual days are consecutive, so too her childbirth days are consecutive.
Analogy
The comparison to menstrual impurity establishes that the seven childbirth-impurity days must be consecutive.