Leviticus 16:2-4

2The Most Holy Place in the Tent of Meeting is behind the curtain. The Lord said to Moses, ‘Your brother Aaron cannot go behind the curtain at any time that he wants to. Tell him that. The Lord appears in a cloud over the lid of the Covenant Box. So Aaron will die if he does not obey the Lord.

3This is how Aaron must go into the Most Holy Place. He must bring a young bull for a sin offering. He must also bring a male sheep for a burnt offering.

4He must wash his body before he puts on his special clothes. He must wear his linen robe and linen clothes next to his body. They are holy. He must tie a linen belt round his body. He must put the linen hat on his head. These clothes are holy.