The story of Marsyas' punishment by Apollo is told in Ovid's Metamorphoses, Book 6, ll. 382–400.
When whoever it was had told of the destruction of the Lycian men, another recalled the story of the satyr Marsyas. Apollo had beaten him in a contest of playing Minerva's reed pipe, and added to the defeat a punishment.
'Why do you tear me from myself?' Marsyas had said, and then screamed, 'Ah! I repent! A pipe is not worth so much!'
As he screamed, his skin was ripped from the surface of his limbs. There was nothing but one big wound. Blood flowed everywhere and the sinews lay open, uncovered, while the trembling, skinless veins gleamed. You could count the pulsing guts and shining innards in his breast.
The country-dwellers, woodland deities, fauns and his brother satyrs all wept for Marsyas. So did his dear friend Olympus, and the nymphs, and every shepherd who pastured his wool-bearing or horned herds on those hills.
He soaked the fertile ground, and the soaked earth drew in his falling tears and drank them deep into her veins, where she made them into water and sent them out into the open air. From this the swift current in its sloping banks made for the sea, and took the name Marsyas – the clearest flowing river in Phrygia.
A bronze in the Fitzwilliam [M.36-1997] shows the poor satyr in happier days, playing his double pipe.