Numbers 3:36

3:36 The appointed responsibilities of the Merarites included the frames of the tabernacle, its crossbars, its posts, its sockets, its utensils, plus all the service connected with these things,

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.