In scene i, Banquo wonders aloud about the prophecies and admits he does not trust Macbeth:BANQUO: Thou hast it now: King, Cawdor, Glamis, all,
In scene 3, the murderers attack Banquo. The dialogue is not as thick as in other scenes, but when the murderer complains that Macbeth doesn't trust him, this is foreshadowing Macbeth's own dissent into madness, and a paranoia that no one is trustworthy:
The foreshadowing of Macbeth's downfall comes further in scene 4, as Macbeth faces off against the "ghost" of Banquo that only he can see. The following line in particular gives a hint that Macbeth's crime will itself be avenged - and the method of that revenge (the coming of the soldiers in the way that makes the trees seem to move).
MACBETH: It will have blood: they say blood will have blood.
Stones have been known to move and trees to speak;