신명기 23:12의 주석

והיה לפנות ערב BUT IT SHALL BE WHEN EVENING COMETH ON, [HE SHALL LAVE HIMSELF WITH WATER] — He should immerse himself close before the setting of the sun, for under no circumstances is he clean without having waited for the sunset (cf. Sifrei Devarim 256:2).

He does not become pure without the setting of the sun. Meaning, he can certainly immerse himself whenever he wants [during] the entire day. But, Rashi wants to explain that when the verse writes, “As sunset nears he is to immerse in water,” you should not say that he cannot do so before this. Rather the verse is giving good advice as it writes afterwards, “And after the sun has set he may enter the midst of the camp.” Since before sunset he remains defiled, why then should he immerse himself when it is still broad daylight? Therefore Rashi says, “Close to the setting of the sun he should immerse himself, as he does not become pure, etc.