What! can the devil speak true? - Banquo and Witches

What! can the devil speak true?

– William Shakespeare

Macbeth, Act 1, Scene 3. Banquo is amazed that the Witches spoke the truth with the prediction that Macbeth would be Thane of Cawdor. He also recognizes that the Witches are evil because they are the devil’s mouthpiece.