Exodus 29:9

29:9 and wrap the sashes around Aaron and his sons and put headbands on them, and so the ministry of priesthood will belong to them by a perpetual ordinance. Thus you are to consecrate Aaron and his sons.

Leviticus 10:12

Perpetual Statutes Moses spoke to Aaron

10:12 Then Moses spoke to Aaron and to Eleazar and Ithamar, his remaining sons, “Take the grain offering which remains from the gifts of the Lord and eat it unleavened beside the altar, for it is most holy.

Numbers 16:39-40

16:39 So Eleazar the priest took the bronze censers presented by those who had been burned up, and they were hammered out as a covering for the altar. 16:40 It was a memorial for the Israelites, that no outsider who is not a descendant of Aaron should approach to burn incense before the Lord, that he might not become like Korah and his company – just as the Lord had spoken by the authority of Moses.

Numbers 18:7

18:7 But you and your sons with you are responsible for your priestly duties, for everything at the altar and within the curtain. And you must serve. I give you the priesthood as a gift for service; but the unauthorized person who approaches must be put to death.”