Leviticus 16:3-4

“When Aaron enters the sanctuary area, he must follow these instructions fully. He must bring a young bull for a sin offering and a ram for a burnt offering. He must put on his linen tunic and the linen undergarments worn next to his body. He must tie the linen sash around his waist and put the linen turban on his head. These are sacred garments, so he must bathe himself in water before he puts them on.