Exodus 28:42-43

New Revised Standard Version, Anglicised

⁴² You shall make for them linen undergarments to cover their naked flesh; they shall reach from the hips to the thighs; ⁴³ Aaron and his sons shall wear them when they go into the tent of meeting, or when they come near the altar to minister in the holy place; or they will bring guilt on themselves and die. This shall be a perpetual ordinance for him and for his descendants after him.