Exodus 28:40-43

40"For Aaron's sons you shall make coats and sashes and caps. You shall make them for glory and beauty.

41And you shall put them on Aaron your brother, and on his sons with him, and shall anoint them and ordain them and consecrate them, that they may serve me as priests.

42You shall make for them linen undergarments to cover their naked flesh. They shall reach from the hips to the thighs;

43and they shall be on Aaron and on his sons when they go into the tent of meeting or when they come near the altar to minister in the Holy Place, lest they bear guilt and die. This shall be a statute forever for him and for his offspring after him.