Numbers 3:13-15

Complete Jewish Bible

¹³ All the firstborn males belong to me, because on the day that I killed all the firstborn males in the land of Egypt, I separated for myself all the firstborn males in Isra’el, both human and animal. They are mine; I am Adonai.”

(v) ¹⁴ Adonai said to Moshe in the Sinai Desert, ¹⁵ “Take a census of the tribe of Levi by clans and families. Count every male a month old or over.”