Numbers 3:12,40-45
And I, behold, I have taken the Levites from among the children of Israel instead of all the firstborn that opens the matrix among the children of Israel: therefore the Levites shall be mine;
Nave's Topical Index—AKJV

Numbers 8:16-18
For they are wholly given to me from among the children of Israel; instead of such as open every womb, even instead of the firstborn of all the children of Israel, have I taken them to me.
Nave's Topical Index—AKJV