Numbers 31:4-8

Of every tribe a thousand, throughout all the tribes of Israel, shall ye send to the war.

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

And Moses sent them to the war, a thousand of every tribe, them and Phinehas the son of Eleazar the priest, to the war, with the holy instruments, and the trumpets to blow in his hand.

And they warred against the Midianites, as the LORD commanded Moses; and they slew all the males.

And they slew the kings of Midian, beside the rest of them that were slain; namely, Evi, and Rekem, and Zur, and Hur, and Reba, five kings of Midian: Balaam also the son of Beor they slew with the sword.