Numbers 1:3-5

Amplified Bible

³ from twenty years old and upward, all in Israel who are able to go out to war. You and Aaron shall number them, army by army. ⁴ And with you there shall be a man [to assist you] from each tribe, each being the head of his father’s household. ⁵ These then are the names of the men who shall stand with you: from [the tribe of] Reuben, Elizur the son of Shedeur;