Rashi on Leviticus 12:7/רש"י על ויקרא י״ב:ז׳

1והקריבו AND HE SHALL OFFER IT — Two offerings have been mentioned, a lamb and a bird, but it states here ,,and he shall offer it and so make an atonement for her” — this teaches you that only the omission to sacrifice a particular one of these two precludes her from eating the sacrificial food. And which is this? It is the sin-offering, because it is stated immediately afterwards: “he shall make expiation for her and she shall be clean” — that which is intended as expiation (i. e. the sin-offering), upon it does the purification depend (Sifra, Tazria Parashat Yoledet, Chapter 3 4).

2וטהרה AND SHE SHALL BE CLEAN — it follows, therefore, that until now (until she has brought the atonement offering) she is termed ‘‘unclean” (i.e. she is regarded as טמאה) although she is actually טהרה.