The Duties of the Heart, by Rabbi Bachye, tr. by Edwin Collins, [1909], at sacred-texts.com
The Danger of Pride and Self-Righteousness
Many whose intention is to do right and serve God are not on their guard against things that destroy this service, and the cause of destruction enters, without their perceiving whence it comes. Thus, one of the Pious (Chassideem) said to his pupils: "If you had no iniquities, I should fear for you that which is greater than iniquities." They said to him: "What is greater than iniquities?" He replied: "Pride and haughtiness."
Man may strive to awaken his intelligence, so that it will make clear to him what the Creator has planted within his mind, by practising the praise of truth, contempt for falsehood, the choice of righteousness, and departure from iniquity.