Numbers 1:1-3

1 And 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 came out of the land of Egypt, saying,

2 Take ye the sum of all the congregation of the sons of Israel, by their families, by their fathers' houses, according to the number of the names, every male, by their polls,

3 from twenty years old and upward, all who are able to go forth to war in Israel. Thou and Aaron shall number them by their armies.