Exodus 28:39-43

Make Aaron's robe and turban of fine linen and decorate his sash with fine needlework. Since Aaron's sons are priests, they should also look dignified. So make robes, sashes, and special caps for them. Then dress Aaron and his sons in these clothes, pour olive oil on their heads, and ordain them as my priests. Make linen shorts for them that reach from the waist down to the thigh, so they won't expose themselves. Whenever they enter the sacred tent or serve at the altar or enter the holy place, they must wear these shorts, or else they will be guilty and die. This same rule applies to any of their descendants who serve as priests.