I Samuel 17:48-51 (NKJV)
[49] Then David put his hand in his bag and took out a stone; and he slung it and struck the Philistine in his forehead, so that the stone sank into his forehead, and he fell on his face to the earth.
[50] So David prevailed over the Philistine with a sling and a stone, and struck the Philistine and killed him. But there was no sword in the hand of David.
[51] Therefore David ran and stood over the Philistine, took his sword and drew it out of its sheath and killed him, and cut off his head with it.