Leviticus 16:
1 Now the Lord spoke to Moses after the death of the two sons of Aaron, when they offered profane fire before the Lord, and died;
2 and the Lord said to Moses: Tell Aaron your brother not to come at just any time into the Holy Place inside the veil, before the Ark cover which is on the ark, lest he die; for I will appear
in the cloud above the Ark cover.
3 Thus Aaron shall come into the Holy Place: with the blood of a young bull as a sin offering, and
of a ram as a burnt offering.
4 He shall put the holy linen tunic and the linen trousers on his body; he shall be girded with a
linen sash, and with the linen turban he shall be attired. These are holy garments.
Therefore he shall wash his body in water, and put them on.