Exodus 30:21
They are to wash their hands and their feet so that they don't die, and it is to be for them a perpetual ordinance for Aaron and his seed from generation to generation."
Exodus 28:43
They shall be on Aaron and his sons when they enter the Tent of Meeting or when they approach the altar to minister in the Holy Place so they don't incur guilt and die. This is to be a perpetual ordinance for him and for his descendants after him."
Exodus 27:21
In the Tent of Meeting, outside the curtain that is before the Testimony, Aaron and his sons are to maintain the lamp stand from evening until morning in the LORD's presence. It is to be a perpetual ordinance from generation to generation among the Israelis."