Numbers 31:3-6

Moses spoke to the people, saying, “Arm men from among you for the war, that they may go against Midian to execute the LORD’S vengeance on Midian. A thousand from each tribe of all the tribes of Israel you shall send to the war.” So there were furnished from the thousands of Israel, a thousand from each tribe, twelve thousand armed for war. Moses sent them, a thousand from each tribe, to the war, and Phinehas the son of Eleazar the priest, to the war with them, and the holy vessels and the trumpets for the alarm in his hand.