Macbeth: which character said this?

I think it's Macbeth talking to the Missus. He's telling her that he can't in good conscience kill King Duncan because 1. they're related; 2. Duncan's the freakin' KING and owns Macbeth's loyalty; and 3. Macbeth is playing host, and as such should be keep keeping any potential ins out, not doing the deed himself.