"He advised me: If I should understand that a demon in the form of a man has come as if to teach me, then I need to say, "If you are from God, then say along with me, 'Lord Jesus Christ, Son of God, have mercy on me a sinner,'" for the enemy does not want to say, 'Have mercy on me.' All who have the Jesus prayer can bind the demon with it; however, the enemy nevertheless prepares many temptations for such a person, and the enemy can only be completely conquered through humility and repentance."
- Father Proclus (Niceu)
Reference: http://www.pravoslavie.ru/english/47107.htm
