Leviticus 16:2-4 ▼

2 And the LORD said to Moses: “Tell your brother Aaron not to enter freely into the Most Holy Place behind the veil in front of the mercy seat on the ark, or else he will die, because I appear in the cloud above the mercy seat.

3 This is how Aaron is to enter the Holy Place: with a young bull for a sin offering and a ram for a burnt offering.

4 He is to wear the sacred linen tunic, with linen undergarments. He must tie a linen sash around him and put on the linen turban. These are holy garments, and he must bathe himself with water before he wears them.