Oedipus tells Jocasta, his wife (and mother, though he does not know this yet), that some drunk guy at a banquet a long time ago shouted out, saying that Oedipus was not really the son of Polybus of Corinth, as he'd been raised to believe. He could not let it go, despite his parents' attempts to comfort him, and so he went to the oracle at Delphi himself, we assume to find out if what this drunkard said was true. Rather than answer his questions, however, he says that Apollo, via the oracle, offered him
Woes, lamentations, mourning, portents dire;
To wit I should defile my mother's bed
And raise up seed too loathsome to behold,
And slay the father from whose loins I sprang.
In other words, the oracle told Oedipus that he would have sexual intercourse with his mother ("defiling her bed"), that he would father children by her (the "loathsome seed" he would "raise up"—the children are loathsome because they are the product of incest), and that he would actually kill his natural father (from "whose loins" Oedipus was produced).