Numbers 8:22

And after that went the Levites in
Into the court of the tabernacle, being at the door of it when the above rites and ceremonies of their consecration were performed: to do their service in the tabernacle of the congregation, before
Aaron and his sons;
in their presence, and by their order, as they should direct them: as the Lord had commanded Moses, so did they unto them;
Aaron and his sons did to the then present Levites according to the command of God by Moses; they exactly observed every punctilio of it, and complied with it; and this the sons of Aaron did continually to the sons of the Levites, as Aben Ezra remarks, in all succeeding ages; when the Levites were consecrated to their service, the same things were done unto them that are here ordered.