I'm pretty sure it's the one about him being great and him becokming king. Just look through them and see which one happens first if this doesn't help
In Macbeth the witches' prophecy that is quickly reveleaded to come true is the one Macbeth and Banquo, back from the battlefied, hear the witches tell him : that he will become thane of Cawdon - thane is a rank of the Scotish nobility-. Macbeth is sceptical about this prophecy but it is quickly revealead as true when King Duncan's men come to tell Macbeth that he has been recently become thane of Cawdon.