In Act III (scene i) of Macbeth, Macbeth is speaking to the murderers he has hired to murder Banquo and Fleance (in order to prevent the prophecy of Banquo's children becoming kings). Now that Macbeth has taken the throne, by killing Duncan, he does not want anyone to take the crown from him. Given that the prophecy was right regarding Macbeth becoming king, he is not risking the rise of power by Fleance.
That being said, in order to insure that the murderers do their job, Macbeth tells them that it was Banquo's fault that they were not promoted. By doing this, Macbeth is able to incite revenge in the murderers.
Have you consider'd of my speeches? Know
That it was he, in the times past, which held you
So under fortune.
Not only does Macbeth tell the men that Banquo was responsible for keeping them from being promoted, he also tells them it is Banquo's fault their families are poor and they, themselves, have been declared to be put to death.
Do you find
Your patience so predominant in your nature,
That you can let this go? Are you so gospell'd,
To pray for this good man and for his issue,
Whose heavy hand hath bow'd you to the grave
And beggar'd yours for ever?
One last way that Macbeth arouses the murderers is by saying they are not men (similar to how Lady Macbeth aroused Macbeth in order to insure Duncan's death). The murderers, after Macbeth questions them, state "we are men, my liege."