For a quote about ambition in Macbeth, take a look at Act I, Scene III. After meeting with the witches and hearing their prophecies, Macbeth is consumed by ambition. In fact, he is so consumed by ambition that he begins thinking about killing Duncan so that he can take the crown for himself:
My thought, whose murder yet is but fantastical,
Shakes so my single state of man
That function is smother'd in surmise,
and nothing is but what is not.
Later, in Act I, Scene IV, Macbeth makes it very clear that he will stop at nothing to become the king of Scotland. When Duncan names his son Malcolm as his heir, for example, Macbeth's naked ambition comes to the fore:
The Prince of Cumberland! That is a step
On which I must fall down, or else o'erleap,
For in my way it lies.
Immediately following this, Macbeth asks nature to disguise his ambition so that his true motives will go undetected:
Stars, hide your fires;
Let not light see my black and deep desires.
In Act I, Scene V, you can also find an example of Lady Macbeth's ambition. When she hears about the prophecies, for instance, she, too, begins thinking of murdering Duncan. In this quote, we not only see the extent of her ambition but also of her ruthlessness, a trait which she plans on using to ensure her husband's success:
Hie thee hither,
That I may pour my spirits in thine ear
And chastise with the valor of my tongue
All that impedes thee from the golden round.