Exodus 28:42-43

New Century Version

⁴² “Make for them linen underclothes to cover them from the waist to the upper parts of the legs. ⁴³ Aaron and his sons must wear these underclothes when they enter the Meeting Tent and anytime they come near the altar to serve as priests in the Holy Place. If they do not wear these clothes, they will be guilty of wrong, and they will die. This will be a law that will last from now on for Aaron and all his descendants.