Numbers 4:5; Numbers 18:7

Numbers 4:5

5 "When the camp sets out, Aaron and his sons shall go in and they shall take down the veil of the screen and cover the ark of the testimony with it;

Numbers 18:7

7 "But you and your sons with you shall attend to your priesthood for everything concerning the altar and inside the veil, and you are to perform service. I am giving you the priesthood as a bestowed service, but the outsider who comes near shall be put to death."