Numbers 1:18-20

New Century Version

¹⁸ and called all the people of Israel together on the first day of the second month. Then the people were listed by their families and family groups, and all the men who were twenty years old or older were listed by name. ¹⁹ Moses did exactly what the Lord had commanded and listed the people while they were in the Desert of Sinai.

²⁰ The tribe of Reuben, the first son born to Israel, was counted; all the men twenty years old or older who were able to serve in the army were listed by name with their families and family groups.