1 Samuel 17:48-51

48When the Philistine started forward to attack him, David ran quickly to the battle line to meet the Philistine.

49David put his hand in the bag, took out a stone, slung it, and hit the Philistine on his forehead. The stone sank into his forehead, and he fell facedown to the ground.

50David defeated the Philistine with a sling and a stone. David overpowered the Philistine and killed him without having a sword.

51David ran and stood over him. He grabbed the Philistine’s sword, pulled it from its sheath, and used it to kill him. Then he cut off his head. When the Philistines saw that their hero was dead, they fled.