Numbers 31:5

So there were delivered out of the thousands of Israel, a thousand of every tribe, twelve thousand armed for war.

There were delivered - i:e., draughted, chosen, an equal amount from each tribe, to prevent the outbreak of mutual jealousy or strife. Considering the numerical force of the enemy, this was a small quota to furnish. But the design was to exercise their faith, and animate them to the approaching invasion of Canaan.