Exodus 28:41-43

Complete Jewish Bible

⁴¹ With them clothe your brother Aharon and his sons. Then anoint them, inaugurate them, and consecrate them, so that they will be able to serve me in the office of cohen. ⁴² Also make for them linen shorts reaching from waist to thigh, to cover their bare flesh. ⁴³ Aharon and his sons are to wear them when they go into the tent of meeting and when they approach the altar to minister in the Holy Place, so that they won’t incur guilt and die. This is to be a perpetual regulation, both for him and for his descendants.