The only time where Banquo comes in contact with the witches is in the first act (scene three) of William Shakespeare's Macbeth. During this dialogue, Banquo asks the witches to address him alone (because Macbeth is fearful of them).
After this, the witches hail Banquo three times and provide him with three prophecies of his own: 1) he is "lesser than Macbeth, and greater"; 2) "not so happy, yet happier"; and 3) that he will get kings, but not be one himself. Two paradoxes exist within the witches' reply to Banquo: lesser/greater and not happy/happier.
Lesser and Greater
Banquo is lesser of a man because of his lack of title, yet he is greater of a man because of his character.
Not Happy and Happy
Banquo is not happy because he knows Macbeth to be the murderer of Duncan. He is happy because he is able to enact his revenge upon Macbeth (during his ghostly visit to Macbeth's dinner). Secondly (although he will not be king (not happy)), Banquo will have a family who will possess a line of kings (happy).