Exodus 28:40-43

⁴⁰“For Aaron’s sons you shall make tunics and sashes and [ornamental] caps, for glory and honor and beauty. ⁴¹You shall put the various articles of clothing on Aaron your brother and on his sons with him, and shall anoint them and ordain and sanctify them, so that they may serve Me as priests. ⁴²You shall make for them [white] linen undergarments to cover their bare flesh, reaching from the waist to the thighs. ⁴³The various articles of clothing shall be on Aaron and on his sons when they enter the Tent of Meeting, or when they approach the altar [of incense] to minister in the Holy Place, so that they do not incur guilt and die. It shall be a statute forever to Aaron and to his descendants after him.