Numbers 1:16-20

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

¹⁷And Moses and Aaron took these men that are pointed out by name.

¹⁸And they assembled all the congregation together on the first day of the second month, and they declared their pedigrees after their families, by their fathers' houses, according to the number of names, from twenty years old and upward, by their polls.

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

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