Numbers 3:13

Overview - Numbers 3
1	The sons of Aaron.
5	The Levites are given to the priests instead of the first-born;
14	are numbered by their families.
21	The families, number, and charge of the Gershonites;
27	of the Kohathites;
33	of the Merarites.
38	The place and charge of Moses and Aaron.
40	The first-born are freed by the Levites.
44	The overplus are redeemed.

Numbers 3:13  (King James Version)
Because all the firstborn are mine; for on the day that I smote all the firstborn in the land of Egypt I hallowed unto me all the firstborn in Israel, both man and beast: mine shall they be: I am the LORD.