Exodus 28:42-43 Christian Standard Bible (CSB)
42 Make them linen undergarments to cover their naked bodies; they must extend from the waist to the thighs. 43 These must be worn by Aaron and his sons whenever they enter the tent of meeting or approach the altar to minister in the sanctuary area, so that they do not incur guilt and die. This is to be a permanent statute for Aaron and for his future descendants.
Exodus 39:27-29 Christian Standard Bible (CSB)
The Other Priestly Garments
27 They made the tunics of fine woven linen for Aaron and his sons. 28 They made the turban and the ornate headbands[a] of fine linen, the linen undergarments of finely spun linen, 29 and the sash of finely spun linen expertly embroidered with blue, purple, and scarlet yarn. They did just as the Lord had commanded Moses.