Halakha Imamat 21:15: Mishneh Torah, Negative Mitzvot & Sefer HaChinukh

That the High Priest shall not cohabit with a widow, even without marriage, because he profanes her, and it is said, “Neither shall he profane his seed among his people” (ibid. 21:15). He is thus prohibited from profaning one who would be eligible to be married to a priest.

That the ordinary priest shall not defile himself by contact with any dead, other than immediate relatives, as it is said, “There shall none be defiled among his people” (Lev. 21:1-3).

That a high priest not have intercourse with a widow: That a high priest not have intercourse with a widow — and even without designation (kiddushin), as it is stated (Leviticus 21:15), “And he shall not profane his seed among his people.” And they said in Kiddushin 78a, “A high priest with a widow is lashed two [sets], on account of ‘he shall not take,’ and on account of ‘he shall not profane’” — meaning that if he married her and had intercourse with her, he is lashed two [sets of] lashes. But if he had intercourse with her without having designated her, he is lashed on account of “he shall not profane”; and like Rava says there: “Rava concedes in [the case of] a high priest with a widow, that if he had intercourse and did not designate [her], he is lashed. What is the reason? As [the Torah] states, ‘And he shall not profane his seed,’ and behold, he profaned.” If he designated her and did not have intercourse with her, he is not lashed on account of “he shall not take” — as behold, we say there, “For what reason is he commanded ‘he shall not take?’ On account of ‘he shall not profane.’” It is implied that the whole time that he does not profane, he is not lashed.