What quote(s) from Macbeth talks about why Macbeth killed Duncan and Banquo?

He decides to kill Duncan in the first act, and his quote
that supports his fears is in Act I, sc 4.  He is not happy that Malcolm is next in
line, so he must move quickly if he is to kill
Duncan.

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The Prince of Cumberland! that is a
step
On which I must fall down, or else
o'erleap,
For in my way it lies. Stars, hide your
fires;
Let not light see my black and deep
desires:
The eye wink at the hand; yet let that
be,
Which the eye fears, when it is done, to
see.
 

Then
in Act III, sc 1, he asks Banquo where he's riding, when he'll be back, and if his son
is going.  He is setting up the murder of Banquo at this point.  This is his quote from
that scene:

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Our fears in
Banquo
Stick deep; and in his royalty of
nature
Reigns that which would be fear'd: 'tis much he
dares;
And, to that dauntless temper of his
mind,
He hath a wisdom that doth guide his
valour
To act in safety. There is none but
he
Whose being I do fear: and, under
him,
My Genius is
rebuked.