Exodus 30:21
they must wash their hands and their feet so that they do not die. And this will be a perpetual ordinance for them and for their descendants throughout their generations."
Exodus 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 27:21
In the tent of meeting outside the curtain that is before the testimony, Aaron and his sons are to arrange it from evening to morning before the Lord. This is to be a lasting ordinance among the Israelites for generations to come.