I Samuel 17:31-36

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.”