Numbers 1:1-3

1The Lord spoke to Moses in the wilderness of Sinai, in the tent of meeting, on the first day of the second month, in the second year after they had come out of the land of Egypt, saying,

2"Take a census of all the congregation of the people of Israel, by clans, by fathers' houses, according to the number of names, every male, head by head.

3From twenty years old and upward, all in Israel who are able to go to war, you and Aaron shall list them, company by company.