Numbers 31:3-5

31:3 So Moses spoke to the people: “Arm men from among you for the war, to attack the Midianites and to execute the Lord’s vengeance on Midian. 31:4 You must send to the battle a thousand men from every tribe throughout all the tribes of Israel.” 31:5 So a thousand from every tribe, twelve thousand armed for battle in all, were provided out of the thousands of Israel.