2 Corinthians 12:6-7

though if I should wish to boast, I would not be a fool, for I would be speaking the truth; but I refrain from it, so that no one may think more of me than he sees in me or hears from me. So to keep me from becoming conceited because of the surpassing greatness of the revelations, a thorn was given me in the flesh, a messenger of Satan to harass me, to keep me from becoming conceited.