Numbers 1:18-20

Amplified Bible

¹⁸ and assembled all the congregation on the first day of the second month, and they registered by ancestry in their families (clans), by their fathers’ households, according to the number of names from twenty years old and upward, head by head, ¹⁹ just as the Lord had commanded Moses. So he numbered them in the Wilderness of Sinai.

²⁰ The sons of Reuben, Israel’s (Jacob’s) firstborn, their generations, by their families (clans), by their fathers’ households, according to the number of names, head by head, every male from twenty years old and upward, all who were able to go to war: