Numbers 31:1-6

1And Jehovah spoke to Moses, saying,

2Avenge the children of Israel upon the Midianites; afterwards shalt thou be gathered unto thy peoples.

3And Moses spoke to the people, saying, Arm from amongst you men for military service, that they go against Midian to execute Jehovah's vengeance upon Midian.

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

5And there were levied out of the thousands of Israel, a thousand by tribe, twelve thousand armed for war.

6And Moses sent them to the war, a thousand by the tribe, them and Phinehas the son of Eleazar the priest, to the war, and the holy instruments, even the alarm-trumpets in his hand.