1 Samuel 17:33 (KJV)

And when the words were heard which David spake, they rehearsed them before Saul: and he sent for him.

And David said to Saul, Let no man’s heart fail because of him; thy servant will go and fight with this Philistine.

And Saul said to David, Thou art not able to go against this Philistine to fight with him: for thou art but a youth, and he a man of war from his youth.

And David said unto Saul, Thy servant kept his father’s sheep, and there came a lion, and a bear, and took a lamb out of the flock:

And I went out after him, and smote him, and delivered it out of his mouth: and when he arose against me, I caught him by his beard, and smote him, and slew him.