I Samuel 17:29-33

And David said, “What have I done now? Is there not a cause?” Then he turned from him toward another and said the same thing; and these people answered him as the first ones did. 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.”