Act 1, Scene 3, Macbeth and Banquo see the witches and listen to what they have to say. The witches tell Macbeth the prophecy, that he will become Thane of Glamis, Thane of Cawdor, and King of Scotland.
Act 1, Scene 7, Macbeth tells Lady Macbeth he has decided not to murder Duncan. Unpleased, Lady Macbeth accuses him of inconstancy, cowardice, and unmanliness. Macbeth finally agrees to proceed with the plan.
Act 2, Scene 1, after Banquo leaves, Macbeth sees the "air-drawn dagger", showing the struggles he faces between his conscience and his ambition.
Act 2, Scene 2, Macbeth proceeds with and completes the plans of killing Duncan.
Act 3, Scene 1, Macbeth filled with his lust for power sees Banquo's prophecy as a threat, so he hired two murderers to kill Banquo (and his child Fleance, who escapes).
Act 3, Scene 4, Macbeth sees the ghost of Banquo in his place at the banquet. His hallucination reveals his unstable mental state and his overwhelming fear.