I Samuel 17:31-37

Now when the words which David spoke were heard, they reported them to Saul; and he sent for him. 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!”