Numbers 8:22
And after that went the Levites in to do their service in the tabernacle of the congregation before Aaron, and before his sons: as the Lord had commanded Moses concerning the Levites, so did they unto them.
Cross-reference
Numbers 8:5-26 contains the full instructions for the Levites' purification and dedication, of which Numbers 8:22 is the concluding execution.
Numbers 8:15 commands the Levites to come do their work after purification; Numbers 8:22 reports that they did so.
Numbers 3:6 originally commands to present the Levites to assist Aaron; Numbers 8:22 shows them finally beginning that service.
Numbers 18:2 reinforces the Levites' role as assistants to Aaron, echoing their service after purification here.
2 Chronicles 30:15-17 shows Levites serving during Hezekiah's Passover, performing rites for the unclean — a later instance of their service role.
2 Chronicles 31:2 describes Hezekiah organizing Levites into divisions for duties, echoing the establishment of their service in Numbers 8:22.
2 Chronicles 35:8-15 recounts Levites preparing Passover sacrifices — another example of them doing their appointed sanctuary work.