Exodus 12:17

12:17 So you will keep the Feast of Unleavened Bread, because on this very day I brought your regiments out from the land of Egypt, and so you must keep this day perpetually as a lasting ordinance.

Exodus 27:21

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.

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.