If it were done, when 'tis done, then 'twere well it were done quickly. Act I, sc. 7.

More from Macbeth

• By the pricking of my thumbs, Something wicked this way comes. 2nd Witch, Act 4, Scene I
• Double, double toil and trouble; Fire burn and cauldron bubble. Act IV, Scene 1
• Fair is foul, and foul is fair. Act I, sc. 1.
• I have no spur to prick the sides of my intent, but only vaulting ambition, which o'erleaps itself, and falls on the other. Act I, sc. 7.
• What's done cannot be undone. Act V, sc. 1.