1 Samuel 17:31-58
31 When the words that David spoke were heard, they repeated them before Saul, and he sent for him. 32 And David said to Saul, “Let no man's heart fail because of him. Your servant will go and fight with this Philistine.” 33 And Saul said to David, “You are not able to go against this Philistine to fight with him, for you are but a youth, and he has been a man of war from his youth.” 34 But David said to Saul, “Your servant used to keep sheep for his father. And when there came a lion, or a bear, and took a lamb from the flock, 35 I went after him and struck him and delivered it out of his mouth. And if he arose against me, I caught him by his beard and struck him and killed him. 36 Your servant has struck down both lions and bears, and this uncircumcised Philistine shall be like one of them, for he has defied the armies of the living God.” 37 And David said, “The Lord who delivered me from the paw of the lion and from the paw of the bear will deliver me from the hand of this Philistine.” And Saul said to David, “Go, and the Lord be with you!”
38 Then Saul clothed David with his armor. He put a helmet of bronze on his head and clothed him with a coat of mail, 39 and David strapped his sword over his armor. And he tried in vain to go, for he had not tested them. Then David said to Saul, “I cannot go with these, for I have not tested them.” So David put them off. 40 Then he took his staff in his hand and chose five smooth stones from the brook and put them in his shepherd's pouch. His sling was in his hand, and he approached the Philistine.
41 And the Philistine moved forward and came near to David, with his shield-bearer in front of him. 42 And when the Philistine looked and saw David, he disdained him, for he was but a youth, ruddy and handsome in appearance. 43 And the Philistine said to David, “Am I a dog, that you come to me with sticks?” And the Philistine cursed David by his gods. 44 The Philistine said to David, “Come to me, and I will give your flesh to the birds of the air and to the beasts of the field.” 45 Then David said to the Philistine, “You come to me with a sword and with a spear and with a javelin, but I come to you in the name of the Lord of hosts, the God of the armies of Israel, whom you have defied. 46 This day the Lord will deliver you into my hand, and I will strike you down and cut off your head. And I will give the dead bodies of the host of the Philistines this day to the birds of the air and to the wild beasts of the earth, that all the earth may know that there is a God in Israel, 47 and that all this assembly may know that the Lord saves not with sword and spear. For the battle is the Lord's, and he will give you into our hand.”
48 When the Philistine arose and came and drew near to meet David, David ran quickly toward the battle line to meet the Philistine. 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 Shaaraim as far as Gath and Ekron. 53 And the people of Israel 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 As soon as Saul saw David go out 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 do not know.” 56 And the king said, “Inquire whose son the boy is.” 57 And as soon as David returned from the striking down 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.” (ESV)