Exodus 28:41-43

41Put these clothes on your brother Aaron and his sons, anoint them, ordain them, and set them apart to serve me as priests.

42“Make linen undergarments to cover them down to their thighs.

43Aaron and his sons must wear them when they go into the tent of meeting or when they come near the altar to serve as priests in the holy place. Then they will be blameless and won’t die. “This is a permanent law for him and his descendants.”