In Act III, Scene 6 the characters Lennox and another unnamed Lord discuss the recent events, murders, and Macbeth's possible involvement. Lennox questions Macbeth's role in Banquo and Duncan's murders. Then he goes on to comment that Macduff must be "in disgrace" with Macbeth, because he left early before Mabeth's banquet:
For from broad words and ’cause he fail'd
His presence at the tyrant's feast, I hear,
Macduff lives in disgrace. (III.6.21-23)
The "tyrant" in Lennox's lines is, of course, Macbeth. The Lord's response informs the audience that Macduff has skipped Macbeth's banquet in order to work against him, yet another reason for Macbeth to be suspicious.
Is gone to pray the holy King, upon his aid
To wake Northumberland and warlike Siward (III.6.30-32)
Macduff has gone to England to seek the aid of the "holy King" (King Edward) that he might lend aid to remove Macbeth from power. As Macbeth becomes increasingly more paranoid and suspicious, he will ultimately target Macduff as a threat to his power and seek to destroy him.