Leviticus 16:3-4

“This is how Aaron is to enter the Most Holy Place: He must first bring a young bull for a sin offering and a ram for a burnt offering. He is to put on the sacred linen tunic, with linen undergarments next to his body; he is to tie the linen sash around him and put on the linen turban. These are sacred garments; so he must bathe himself with water before he puts them on.