Numbers 31:5

³  And Moses spake unto the people, saying, Arm some of yourselves unto the war, and let them go against the Midianites, and avenge the LORD of Midian.

⁴  Of every tribe a thousand, throughout all the tribes of Israel, shall ye send to the war.

⁵  So there were delivered out of the thousands of Israel, a thousand of every tribe, twelve thousand armed for war.

⁶  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.

⁷  And they warred against the Midianites, as the LORD commanded Moses; and they slew all the males.