2 Samuel 5:22-24

But after a while the Philistines returned and again spread out across the valley of Rephaim. And again David asked the LORD what to do. “Do not attack them straight on,” the LORD replied. “Instead, circle around behind and attack them near the poplar trees. When you hear a sound like marching feet in the tops of the poplar trees, be on the alert! That will be the signal that the LORD is moving ahead of you to strike down the Philistine army.”