Exodus 28:42-43

New International Version - UK

⁴² ‘Make linen undergarments as a covering for the body, reaching from the waist to the thigh. ⁴³ Aaron and his sons must wear them whenever they enter the tent of meeting or approach the altar to minister in the Holy Place, so that they will not incur guilt and die.

‘This is to be a lasting ordinance for Aaron and his descendants.