Numbers 1:17-19

17And Moses and Aaron took these men who are expressed by their names,

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

19As Jehovah had commanded Moses, so he numbered them in the wilderness of Sinai.