Numbers 1:17-19

New Revised Standard Version Catholic Edition

¹⁷ Moses and Aaron took these men who had been designated by name, ¹⁸ and on the first day of the second month they assembled the whole congregation together. They registered themselves in their clans, by their ancestral houses, according to the number of names from twenty years old and upward, individually, ¹⁹ as the Lord commanded Moses. So he enrolled them in the wilderness of Sinai.