Numbers 3:40-41

40Adonai said to Moses, “Count every firstborn male of Bnei-Yisrael from one month old and upward and make a list of their names.

41Set the Levites apart for me in place of all the firstborn of Bnei-Yisrael, and, all the livestock of the Levites in place of the firstborn of the livestock of Bnei-Yisrael. I am Adonai.”