What quote in Macbeth supports the idea that it is doubtful Macbeth would have killed anyone without the push given by the witches' prophecies?

After Macbeth hears the two prophecies from the Weird Sisters -- that he will become Thane of Cawdor and then, at some point, king -- he doesn't seem entirely sure about what to think. However, when he is promptly told that Duncan has given him the title of Cawdor, he begins to hope that the greater prediction will come true as well.  To himself, he says, "If chance will have me king, why, chance may crown me / Without my stir" (1.4.158-159).  He hopes that he will not have to do anything to become king, just as he did not have to do anything to become Thane of Cawdor. This line makes it seem as though he doesn't desire to do any harm to Duncan and would never have, had it not been for the sisters. 

Further, on the night of the banquet at the Macbeths' house, Macbeth tells his wife,

"We will proceed no further in this business. / He hath honored me of late, and I have bought / Golden opinions from all sorts of people, / Which would be worn now in their newest gloss, / Not cast aside so soon" (1.7.34-38). 

He does not want to go through with the murder because Duncan has recently honored Macbeth with the new title and because Macbeth has recently earned a great deal of respect from so many people.  He does not want to do anything that would tarnish his reputation or undermine the faith others have placed in him.  This also makes it seem as though he would not have killed anyone were it not for the influence of the sisters.