Sifrei Devarim 255/ספרי דברים רנ״ה

2“A man” (Dt. 23:11)—this excludes a minor from the rule.

3“Who has not purified himself from a nocturnal emission” (Dt. 23:11)—might I infer only thatthe rule applies to an emission by night?How do I know that it applies as well to an emission by day?The Teaching states:“Who has not purified himself” (Dt. 23:11)—from an ejaculation of semen, day or night.If so, why is an emission by night specified?This teaches thatthe verse speaks in common terms.

42. “Then he shall go beyond the camp” (Dt. 23:11)—this is a prescriptive commandment;