Numbers 3:12-13

"I have taken the Levites from the sons of Israel. For the Levites, and all the firstborn who open the womb among the sons of Israel, shall be mine. For every firstborn is mine. From the time that I struck the firstborn in the land of Egypt, I have sanctified for myself whatever is born first in Israel. From man, even to beast, they are mine. I am the Lord."