1 Samuel 17:49-58

49 And David put his hand in his bag and took out a stone, and slung it, and struck the Philistine on his forehead; the stone sank into his forehead, and he fell on his face to the ground.
50 So David prevailed over the Philistine with a sling and with a stone, and struck the Philistine, and killed him; there was no sword in the hand of David.
51 Then David ran and stood over the Philistine, and took 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 champion was dead, they fled.
52 And the men of Israel and Judah rose with a shout and pursued the Philistines as far as Gath and the gates of Ekron, so that the wounded Philistines fell on the way from Sha-ara'im as far as Gath and Ekron.
53 And the Israelites came back from chasing the Philistines, and they plundered their camp.
54 And David took the head of the Philistine and brought it to Jerusalem; but he put his armor in his tent.
55 When Saul saw David go forth against the Philistine, he said to Abner, the commander of the army, "Abner, whose son is this youth?" And Abner said, "As your soul lives, O king, I cannot tell."
56 And the king said, "Inquire whose son the stripling is."
57 And as David returned from the slaughter of the Philistine, Abner took him, and brought him before Saul with the head of the Philistine in his hand.
58 And Saul said to him, "Whose son are you, young man?" And David answered, "I am the son of your servant Jesse the Bethlehemite."