Halakhah for Nazir 42:1

He prohibited the nazirite from entering into the tent of a corpse. And that is His saying, "by a dead body he shall not come" (Numbers 6:6). And in the explanation, they said in the Gemara (Nazir 42b), "Scripture spoke with a categorical verse - 'He shall not become impure' (Numbers 6:7). [Hence] when it states, 'he shall not come,' it is to prohibit him about the impurity and about the entering." And there, they said that when he enters the tent after he becomes impure, he is only lashed once; and that he is only liable for two [sets] if the impurity and the entering were together - for example, if he entered into a house with a sick person and he sat there until that person died. As it comes out that he became impure and he entered the tent [that has a corpse] at the same time. But if he enters the tent of a corpse, the impurity preceded the entrance - as it is explained there, according to the principles that are demonstrated in Ohalot. (See Parashat Nasso; Mishneh Torah, Nazariteship 1.)