Numbers 1:16-20

¹⁶These were the selected of the congregation, the princes of the tribes of their fathers; the heads of the thousands of Israel were they.

¹⁷And Moses and Aaron took these men who are expressed by name:

¹⁸And all the congregation they assembled together on the first day of the second month, and they were enrolled in the lists of their pedigrees after their families, by the descent from their fathers, by numbering the names, from twenty years old and upward, according to their polls.

¹⁹As the Lord had commanded Moses, so did he number them in the wilderness of Sinai.

²⁰And there were of the children of Reuben the first-born of Israel, by their generations, after their families, by the descent from their fathers, by numbering the names according to their polls, every male from twenty years old and upward, all that were able to go forth to war;