What is the Qareen, what is its religion, and is it a disbeliever or a wicked one among Muslims? Does it harm a person with physical or psychological illnesses, or possess them? Does it know what goes on in a person's mind?

The Qareen (companion Jinn) is a devil appointed over a person by Allah's permission, commanding him to indecency and forbidding him from good. If a servant's heart is sound, truthful, and turned towards Allah, then Allah helps him against this Qareen until it becomes unable to mislead him. Therefore, one should seek refuge with Allah from the accursed devil whenever he incites him.