The event in Macbeth that illustrates the recurring motif of "Fair is foul, and foul is fair" is A. Macbeth kills the current king and is rewarded by being named king himself.
He is, of course, hiding the fact that he was the one who killed the king, so as not to be killed himself. Thus, everybody thinks he is a valiant knight who deserves to be on the throne, although he is a vile murderer.
