Numbers 1:16-19

These were the ones chosen from the congregation, the chiefs of their ancestral tribes, the heads of the clans of Israel. Moses and Aaron took these men who had been named, and on the first day of the second month, they assembled the whole congregation together, who registered themselves by clans, by fathers’ houses, according to the number of names from twenty years old and upward, head by head, as the LORD commanded Moses. So he listed them in the wilderness of Sinai.