1 Samuel 17:47-51

and that this entire assembly may know that the LORD does not save with the sword or with the spear; for the battle is the LORD’S and He will hand you over to us.” When the Philistine rose and came forward to meet David, David ran quickly toward the battle line to meet the Philistine. David put his hand into his bag and took out a stone and slung it, and it struck the Philistine on his forehead. The stone penetrated his forehead, and he fell face down on the ground. So David triumphed over the Philistine with a sling and a stone, and he struck down the Philistine and killed him; but there was no sword in David’s hand. So he ran and stood over the Philistine, grasped his sword and drew it out of its sheath and killed him, and cut off his head with it. When the Philistines saw that their [mighty] champion was dead, they fled.