Numbers 3:12, 15, 45

And I, behold, I have taken the Levites from among the children of Israel instead of all the firstborn that openeth the matrix among the children of Israel: therefore the Levites shall be mine

Number the children of Levi after the house of their fathers, by their families: every male from a month old and upward shalt thou number them.

Take the Levites instead of all the firstborn among the children of Israel, and the cattle of the Levites instead of their cattle; and the Levites shall be mine: I am the LORD.