Numbers 1:50

1:50 But appoint the Levites over the tabernacle of the testimony, over all its furnishings and over everything in it. They must carry the tabernacle and all its furnishings; and they must attend to it and camp around it.

Numbers 8:16

8:16 For they are entirely given to me from among the Israelites. I have taken them for myself instead of all who open the womb, the firstborn sons of all the Israelites.