In the banquet scene of Macbeth, Macbeth seats his guests, according to their rank, and consults with the three murderers. The Murderers were sent to kill both Banquo and his son Fleance. This act shows that Macbeth not only believes in the witches predictions, he's willing to kill again to prevent Banquo's sons from inheriting the crown. Unlike the murder of Duncan, Macbeth does not consult with Lady Macbeth, he plans and instigates the murder entirely on his own.
After Macbeth applauds the murderes for having Banquo's blood on their faces, the murderers report that they have killed Banquo, but that Fleance has gotten away.
Thou art the best o’ the cut-throats! Yet he's good
That did the like for Fleance. If thou didst it,
Thou art the nonpariel.
Most royal sir,
Fleance is 'scaped.
Macbeth's reaction shows that he is angry that Fleance has escaped, but is happy that Banquo is dead. He knows to remain vigilant for Fleance, as he is still alive he poses a threat to Macbeth and his crown.
MACBETH: Thanks for that.
There the grown serpent lies; the worm that's fled
Hath nature that in time will venom breed,
No teeth for the present. Get thee gone. Tomorrow
We'll hear ourselves again.