Then the LORD spoke to Moses in the Wilderness of Sinai, saying:
Numbers 3:14
Surrounding context
3:13 because all the firstborn are Mine. On the day that I struck all the firstborn in the land of Egypt, I sanctified to Myself all the firstborn in Israel, both man and beast. They shall be Mine: I am the LORD."
3:14 Then the LORD spoke to Moses in the Wilderness of Sinai, saying:
3:15 "Number the children of Levi by their fathers' houses, by their families; you shall number every male from a month old and above."