1 Samuel 17:47-57

47 And all this assembly shall know that the Lord saveth not with sword and spear: for it is his battle, and he will deliver you into our hands.
48 And when the Philistine arose, and was coming, and drew nigh to meet David, David made haste, and ran to the fight to meet the Philistine.
49 And he put his hand into his scrip, and took a stone, and cast it with the sling, and fetching it about, struck the Philistine in the forehead, and he fell on his face upon the earth.
50 And David prevailed over the Philistine, with a sling and a stone, and he struck, and slew the Philistine. And as David had no sword in his hand,
51 He ran, and stood over the Philistine, and took his sword, and drew it out of the sheath, and slew him, and cut off his head. And the Philistines seeing that their champion was dead, fled away.
52 And the men of Israel and Juda rising up shouted, and pursued after the Philistines till they came to the valley and to the gates of Accaron, and there fell many wounded of the Philistines in the way of Saraim, and as far as Geth, and as far as Accaron.
53 And the children of Israel returning, after they had pursued the Philistines, fell upon their camp.
54 And David taking the head of the Philistine, brought it to Jerusalem: but his armour he put in his tent.
55 Now at the time that Saul saw David going out against the Philistines, he said to Abner, the captain of the army: Of what family is this young man descended, Abner? And Abner said: As thy soul liveth, O king, I know not.
56 And the king said: Inquire thou, whose son this young man is.
57 And when David was returned, after the Philistine was slain, Abner took him, and brought him in before Saul, with the head of the Philistine in his hand.