Macbeth requests that Banquo come to his feast.
When Macbeth speaks to Banquo, he is already suspicious of him. He fears that Banquo knows that he killed the king. In fact, Banquo fears that Macbeth played “foully” for it, so they are both right! It would therefore be a pretty uncomfortable conversation, as Macbeth pretends not to be suspicious of Banquo and Banquo pretends not to be suspicious of Macbeth.
Macbeth tells Banquo that he is having a banquet, and he expects him to be there.
To-night we hold a solemn supper sir,
And I'll request your presence.
Let your highness
Command upon me; to the which my duties
Are with a most indissoluble tie
For ever knit. (Act 3, Scene 1)
You can tell by Banquo’s response that he is trying to placate Macbeth. He calls him “your highness” and lays on the ‘your wish is my command’ pretty thick. Macbeth casually inquires about his riding, and asks when he will be back, after reminding him again to be back in time.
Fail not our feast.
My lord, I will not. (Act 3, Scene 1)
Macbeth is asking where Banquo is going and reminding him to make it to the dinner because he does not plan for Banquo to actually be at that feast. As soon as he leaves, Macbeth will meet with three murderers and send them after Banquo and his son Fleance. This way, Macbeth can kill two birds with one stone. He gets rid of someone who is suspicious of him, and he takes care of the pesky prophecy about Banquo's sons being king.