Final answer:
The line, "Banquo's buried; he cannot come out on's grave," is spoken by Macbeth in Shakespeare's play when he is haunted by Banquo's ghost.
Step-by-step explanation:
The line, "Banquo's buried; he cannot come out on's grave," is spoken by Macbeth himself. This occurs in a tense moment in William Shakespeare's play, "Macbeth," where Macbeth, now King after a series of murders and deceptions, is haunted by the guilt and fear of his actions. When Banquo's ghost appears at the banquet, only Macbeth can see it, causing him to react in terror. His guests are unaware of the apparition, which leads Macbeth to speak this line in an attempt to reassure himself and explain away his frightened outburst.