1 Samuel 17:50-58

So David prevailed over the Philistine with a sling and with a stone, and smote the Philistine, and slew him; but there was no sword in the hand of David. Then David ran, and stood over the Philistine, and took his sword, and drew it out of the sheath thereof, and slew him, and cut off his head therewith. And when the Philistines saw that their champion was dead, they fled. And the men of Israel and of Judah arose, and shouted, and pursued the Philistines, until thou comest to Gai, and to the gates of Ekron. And the wounded of the Philistines fell down by the way to Shaaraim, even unto Gath, and unto Ekron. And the children of Israel returned from chasing after the Philistines, and they plundered their camp. And David took the head of the Philistine, and brought it to Jerusalem; but he put his armor in his tent. And when Saul saw David go forth against the Philistine, he said unto Abner, the captain of the host, Abner, whose son is this youth? And Abner said, As thy soul liveth, O king, I cannot tell. And the king said, Inquire thou whose son the stripling is. 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. And Saul said to him, Whose son art thou, thou young man? And David answered, I am the son of thy servant Jesse the Beth-lehemite.