Numbers 4:17-19

Young's Literal Translation

¹⁷ And Jehovah speaketh unto Moses and unto Aaron, saying,

¹⁸ `Ye do not cut off the tribe of the families of the Kohathite from the midst of the Levites;

¹⁹ but this do to them, and they have lived, and do not die in their drawing nigh the holy of holies: -- Aaron and his sons go in, and have set them, each man to his service, and unto his burden,