1 Samuel 17:49-50

17:49 David reached his hand into the bag and took out a stone. He slung it, striking the Philistine on the forehead. The stone sank deeply into his forehead, and he fell down with his face to the ground.

17:50 David prevailed over the Philistine with just the sling and the stone. He struck down the Philistine and killed him. David did not even have a sword in his hand.