Numbers 1:17

14 From Gad, Eliasaph, the son of Reuel;

15 From Naphtali, Ahira, the son of Enan.

16 These are the men named out of all the people, chiefs of their fathers' houses, heads of the tribes of Israel.

17 And Moses and Aaron took these men, marked out by name;

18 And they got together all the people on the first day of the second month; and everyone made clear his family and his father's house, by the number of the names, from twenty years old and over.

19 As the Lord had given orders to Moses, so they were numbered by him in the waste place of Sinai.

20 The generations of the sons of Reuben, the oldest son of Israel, were numbered by their families and their fathers' houses, every male of twenty years old and over, who was able to go to war;