2 Samuel 8:1-2

After this, David defeated and subdued the Philistines by conquering Gath, their largest town. David also conquered the land of Moab. He made the people lie down on the ground in a row, and he measured them off in groups with a length of rope. He measured off two groups to be executed for every one group to be spared. The Moabites who were spared became David’s subjects and paid him tribute money.