Cornutus, Commentary on Persius 6.10:
Thus writes Ennius in the beginning of his Annals, where he says that in a dream he saw Homer claiming that he had once been a peacock, and that his soul had been transferred from there into Ennius according to the doctrine of Pythagoras, who said that human souls, through a process of palingenesis (that is, a repeated birth) are able to enter new bodies as they leave their old ones behind. He used the phrase ‘the fifth’ in accordance with the opinion that the soul of Pythagoras was moved into a peacock, from the peacock to Euphorbius, from Euphorbius to Homer, and from Homer to Ennius. Or, to be sure, he said ‘the fifth’ because Ennius was named Quintus.
sic Ennius in Annalium suorum principio, ubi se dicit vidisse in somnis Homerum dicentem fuisse quondam pavonem et ex eo translatam in se animam esse secundum Pytagorae philosophi definitionem, qui dicit animas humanas per palingenesiam, id est per iteratam generationem, exeuntes de corporibus in alia posse corpora introire. ideo autem, “quintus” dixit propter eam opinionem quae dicit animam Pytagorae in pavonem translatam, de pavone vero ad Euphorbium, de Euphorbio ad Homerum, de Homero autem ad Ennium. vel certe quod cognomento Ennius dicitur.