What was the prayer that the cyclops Polyphemus prayed to his father Poseidon?
After arriving in the land of the cyclops, Polyphemus, Odysseus and his men eat some of the wild goats and steal food from a cave containing sheep, milk, and cheese. Although Polyphemus (who inhabits this cave) is initially gracious to these intruders, his good will runs out; he eats two of the men and traps Odysseus and the others, intending to eat them later.
Knowing that they rely on Polyphemus to move the large rock that blocks the entrance of his cave, Odysseus decides not to immediately kill the cyclops. Instead, he hardens a wooden staff in a fire, gets the creature drunk, and stabs it in the eye with the staff. Clinging to Polyphemus' sheep, they are able to escape when the now blind cyclops lets them out of the cave.
After discovering Odysseus' identity and that he has managed to get loose, Polyphemus cries out a prayer to his father, Poseidon:
Hear me, Poseidon, earth-enfolder, thou dark-haired god, if indeed I am thy son and thou declarest thyself my father; grant that Odysseus, the sacker of cities, may never reach his home, even the son of Laertes, whose home is in Ithaca; but if it is his fate to see his friends and to reach his well-built house and his native land, late may he come and in evil case, after losing all his comrades, in a ship that is another's; and may he find woes in his house.
In other words, Polyphemus is asking that Poseidon prevent Odysseus from being able to return to his homeland, or at the very least, that he may arrive late, lose his friends, and see the security of his household threatened in the interim. This, of course, comes to pass, and the details of Odysseus' ten-year journey home are what comprise the bulk of The Odyssey.
Polyphemus prayed to his father Poseidon that Odysseus never get home. If he did make it home, let it be many years away. He also prayed for Odysseus to lose all of his men/companions. Then once he arrived home, he was to face "bitter days." All of these prayers were granted. It took him 10 years to return, all his men were killed, and the suitors were taking over his home/wife.