Exodus 28:35

28:35 The robe is to be on Aaron as he ministers, and his sound will be heard when he enters the Holy Place before the Lord and when he leaves, so that he does not die.

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.