Numbers 3:11-13

The LORD also said to Moses, “I have taken the Levites from among the Israelites. I have taken them in place of the son born first to each woman in Israel. The Levites belong to me. That’s because every male born first to a mother is mine. In Egypt I struck down all the males born first. I did it when I set apart for myself every male born first to a mother in Israel. That is true for men and animals alike. They belong to me. I am the LORD.”