Pausanias Description of Greece 1.30.3

[3]
  Not far from the Academy is the monument of Plato, to whom heaven foretold that he would be the prince of philosophers. The manner of the foretelling was this. On the night before Plato was to become his pupil Socrates in a dream saw a swan fly into his bosom. Now the swan is a bird with a reputation for music, because, they say, a musician of the name of Swan became king of the Ligyes on the other side of the Eridanus beyond the Celtic territory, and after his death by the will of Apollo he was changed into the bird. I am ready to believe that a musician became king of the Ligyes, but I cannot believe that a bird grew out of a man.

[3] Not far from the Academy is the tomb [ mnēma] of Plato, to whom the god [ theos] foretold [ pro-sēmainein] that he would be the best [ aristos] when it comes to philosophy. The manner of the foretelling [ pro-sēmainein] was this. On the night before Plato was to become his pupil Socrates dreamed that he saw a swan [ kuknos] fly into his insides [ kolpos]. Now the swan is a bird with a reputation for the art-of-the-Muses [ mousikē], because, they say, a practitioner-of-the-art-of-the-Muses [ mousikos] by the name of Swan [ Kuknos] became king of the Ligyes on the other side of the Eridanos beyond the Celtic territory, and after his death by the will of Apollo he was changed into the bird. I am ready to believe that a practitioner-of-the-art-of-the-Muses [ mousikos] became king of the Ligyes, but I cannot believe that a bird was generated out of a man.