What prophecy was made to the Cyclops (in The Odyssey) that is told in lines 412-426?
An additional note about the prophecy--Polyphemus, who thought very highly of himself, his strength, and great size, was expecting someone his equal in strength to defeat him and blind him. So, when Polyphemus is first blinded, he foolishly does not connect the prophecy with its fulfillment. Not only had Odysseus tricked him by telling him that his name was "Noman" (no man), but Polyphemus did not think that some minuscule human would be able to do such great harm to him.
Unfortunately, Odysseus could not leave well enough alone, and because of his taunting, Polyphemus calls upon the power of his father Poseidon to avenge his blinding (the fulfillment of the prophecy), which of course lengthens Odysseus's journey on the sea even more.
In the part that you are talking about, Odysseus and his men have finally escaped from Polyphemus the cyclops. Or at least some of his men had, others had been killed and eaten.
To escape, they have driven a stake through the cyclops' eye and he is now blind. As they escape, Odysseus taunts Polyphemus and even tells him his name so that the cyclops can know who has blinded him.
When the cyclops hears the name, he tells about the prophecy. The prophecy had said that Polyphemus would be blinded by a man named Odysseus.