I Samuel 17:32-37, 45

Then David said to Saul, “Let no man’s heart fail because of him; your servant will go and fight with this Philistine.” And Saul said to David, “You are not able to go against this Philistine to fight with him; for you are a youth, and he a man of war from his youth.” But David said to Saul, “Your servant used to keep his father’s sheep, and when a lion or a bear came and took a lamb out of the flock, I went out after it and struck it, and delivered the lamb from its mouth; and when it arose against me, I caught it by its beard, and struck and killed it. Your servant has killed both lion and bear; and this uncircumcised Philistine will be like one of them, seeing he has defied the armies of the living God.” Moreover David said, “The LORD, who delivered me from the paw of the lion and from the paw of the bear, He will deliver me from the hand of this Philistine.” And Saul said to David, “Go, and the LORD be with you!”

Then David said to the Philistine, “You come to me with a sword, 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.