Numbers 31:4-6

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.