Exodus 28:39-43

“Weave Aaron's shirt of fine linen and make a turban of fine linen and also a sash decorated with embroidery. “Make shirts, sashes, and caps for Aaron's sons, to provide them with dignity and beauty. Put these clothes on your brother Aaron and his sons. Then ordain them and dedicate them by anointing them with olive oil, so that they may serve me as priests. Make linen shorts for them, reaching from the waist to the thighs, so that they will not expose themselves. Aaron and his sons must always wear them when they go into the Tent of my presence or approach the altar to serve as priests in the Holy Place, so that they will not be killed for exposing themselves. This is a permanent rule for Aaron and his descendants.