Numbers 1:5

1:5 Now these are the names of the men who are to help you:

from Reuben, Elizur son of Shedeur;

Numbers 1:20

1:20 And they were as follows:

The descendants of Reuben, the firstborn son of Israel: According to the records of their clans and families, all the males twenty years old or older who could serve in the army were listed by name individually.