2 Samuel 8:1-2

1In the course of time, David defeated the Philistines and subdued them, and he took Metheg Ammah from the control of the Philistines. 2David also defeated the Moabites. He made them lie down on the ground and measured them off with a length of cord. Every two lengths of them were put to death, and the third length was allowed to live. So the Moabites became subject to David and brought him tribute.