Kommentar zu Wajikra 14:23

ביום השמיני לטהרתו ON TIIE EIGHTH DAY OF HIS BEING PRONOUNCED CLEAN — i. e. the eighth day after the birds have been brought and he has been sprinkled with the cedar stick, the hyssop and the crimson wool (cf. v. 10).

The eighth day from when the birds [were brought] and the sprinkling. Rashi is answering the question: It implies that on this [day], the eighth day from when the birds were brought, he is pure, but this cannot be, for on the eighth day he brings the offerings and, perforce, he is not pure beforehand. Upon this Rashi explains: “The eighth day from [the day when] the birds [were brought]...” and that day is also called purification from causing impurity due to lying down or sitting. You need not ask: How does Rashi know it is the eighth day from the sprinkling? Perhaps it refers to the day of bringing the burnt-offering, sin-offering, and guilt-offering. The answer is: Because it says above (v. 9): “It shall be, that on the seventh day, he shall shave off,” thus, it must be that “the eighth day” refers to [the day after] “the seventh day.” And even though above it also says (v. 10): “On the eighth day, he shall take two lambs...” — and there Rashi does not explain anything — that is because earlier it is written (v. 8): “He must remain, outside of his tent, for seven days,” and [in the next verse] it is written: “It shall be, that on the seventh day,” and then immediately afterwards: “On the eighth day.” [Thus,] it must surely refer to what precedes it.