Rashi on Leviticus 21:11/רש"י על ויקרא כ״א:י״א

1'ועל כל נפשת מת וגו‎‎ means, he shall not go into a tent wherein is a corpse.

2נפשת מת — The word נפשת, which appears redundant, is intended to include a quarter of a log of the blood of a corpse — to intimate that even this, as a corpse itself, makes men and vessels unclean through being in a "tent” in which it happens to be (Sanhedrin 4a).

3לאביו ולאמו לא יטמא NOR SHALL HE DEFILE HIMSELF FOR HIS FATHER OR FOR HIS MOTHER — By these words which appear redundant, since אביו ואמו are included in כל נפשת מת, Scripture has no other intention than to permit him to defile himself for a מת מצוה (cf. v. 1) (Sifra, Emor, Section 2 4; Nazir 47b).