Numbers 1:3-7

From twenty years old and upward, all that are able to go forth to war in Israel: thou and Aaron shall number them by their armies.

And with you there shall be a man of every tribe; every one head of the house of his fathers.

And these are the names of the men that shall stand with you: of the tribe of Reuben; Elizur the son of Shedeur.

Of Simeon; Shelumiel the son of Zurishaddai.

Of Judah; Nahshon the son of Amminadab.