Rashi on Leviticus 21:4/רש"י על ויקרא כ״א:ד׳

1לא יטמא בעל בעמיו להחלו This means: he shall not defile himself for his wife if she is really unfitted to be his wife (because he is a כהן) and through whom he consequently becomes profaned as a priest, so long as she remains with him (Sifra, Emor, Section 1 15). The following, therefore, is the literal exposition of the verse: לא יטמא בעל, a husband shall not defile himself for his wife's corpse while it is among its people, which means that there are persons who can bury her so that she is not a מת מצוה (cf. Rashi’s explanation of בעמיו on v. 1). And with reference to what kind of wife do I say this? With reference to such a one who להחלו, i. e. who leads to his being profaned and therefore disqualified from his priestly duties so long as she remains with him (cf. Sifra, Emor, Section 1 15; Yevamot 90b).