Numbers 9:6
But there were [some] men who were unclean because of a human corpse, so they could not observe the Passover on that day. These men came before Moses and Aaron the same day
Leviticus 21:1
The LORD said to Moses: "Speak to Aaron's sons, the priests, and tell them: A priest is not to make himself ceremonially unclean for a [dead] person among his relatives,
Leviticus 21:2
except for his immediate family: his mother, father, son, daughter, or brother.
Leviticus 21:10-12
"The priest who is highest among his brothers, who has had the anointing oil poured on his head and has been ordained to wear the garments, must not dishevel his hair or tear his garments.
He must not go near any dead person or make himself unclean [even] for his father or mother.
He must not leave the sanctuary or he will desecrate the sanctuary of his God, for the consecration of the anointing oil of his God is on him; I am the LORD.
Ezekiel 44:25
A priest may not come [near] a dead person so that he becomes defiled. However, he may defile himself for a father, a mother, a son, a daughter, a brother, or an unmarried sister.