Numbers 1:1-3

1Now the Lord spoke to Moses in the tent of meeting in the wilderness of Sinai on the first day of the second month of the second year after the Israelites departed from the land of Egypt. He said:

2“Take a census of the entire Israelite community by their clans and families, counting the name of every individual male.

3You and Aaron are to number all in Israel who can serve in the army, those who are twenty years old or older, by their divisions.