Numbers 1:1-3

1In the wilderness of Sinai, on the first day of the second month in the second year from the Exodus from the land of Egypt, Adonai spoke to Moses in the Tent of Meeting saying,

2“Do a head count of all the community of Bnei-Yisrael by their families and their ancestral house, with a total of every male one by one.

3You and Aaron are to muster by their divisions every son from 20 years and upward available to serve in the army of Israel.