Exodus 19:13

19:13 No hand will touch him – but he will surely be stoned or shot through, whether a beast or a human being; he must not live.’ When the ram’s horn sounds a long blast they may go up on the mountain.”

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.