Exodus 28:43

28:43 These must be on Aaron and his sons when they enter to the tent of meeting, or when they approach the altar to minister in the Holy Place, so that they bear no iniquity and die. It is to be a perpetual ordinance for him and for his descendants after him.

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.

Numbers 25:11-13

25:11 “Phinehas son of Eleazar, the son of Aaron the priest, has turned my anger away from the Israelites, when he manifested such zeal for my sake among them, so that I did not consume the Israelites in my zeal. 25:12 Therefore, announce: ‘I am going to give to him my covenant of peace. 25:13 So it will be to him and his descendants after him a covenant of a permanent priesthood, because he has been zealous for his God, and has made atonement for the Israelites.’”