2 Corinthians 12:5-8

On behalf of this man I will boast, but on my own behalf I will not boast, except of my weaknesses— 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. Three times I pleaded with the Lord about this, that it should leave me.