What are some quotes in Shakespeare's Macbeth that show betrayal?

The capacity to betray based on greed and ambition is a
central theme in the work, so quotes on this subject are plentiful.  Here are a
few.

1. Macbeth considers killing the king, the ultimate
form of betrayal, after the witches prophecies begin to come true.  He admits this
desire when he says,

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why do I yield to that suggestion              
                              Whose horrid image doth unfix my hair                    
                    And make my seated heart knock at my ribs,                          
  Against the use of nature? (I,
iii)

He understands that this
betrayal is evil.

2. As the time for murder approaches,
Macbeth runs through the reasons for not killing the king.  The king is his own kin who
trusts Macbeth and has just rewarded his valor in battle.  Yet he decides to kill him
anyway as evidenced by the line,

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I am settled, and bend up                        
                              Each corporal agent to this terrible feat
(I,vii).

Macbeth has allowed
his wife to convince him to commit the murder.

3.  Banquo,
Macbeth's friend who also witnessed and received prophecies, begins to suspect the
betrayal after the murder.  He notes to himself that

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Thou hast it now: king, Cawdor, Glamis, all,    
                            As the weird women promised, and, I fear,                  
              Thou play'dst most foully for't: ( III
i).

However, this realization
is too late.  Macbeth makes yet another betrayal and kills his own friend to secure the
crown for himself.