During Act 2, Scene 2 of the play, Macbeth tells Lady Macbeth that he heard a voice say to him, “Sleep no more! Macbeth does murder sleep!” These words are most likely the result of an auditory hallucination that Macbeth experiences after murdering King Duncan. Technically, aside from Macbeth repeating it to his wife, no character actually says this line. Shakespeare uses these chilling words as an indication that the title character is on the verge of going mad. This much is obvious. More importantly, however, the line serves as a foreshadowing device that gives readers a clue as to the eventual outcome of this murder. Sleep is mentioned often in Macbeth, at times as a comparison to death and at other times a metaphor for peace. In this instance
