Hesiod, Theogony 305–334: Echidna's offspring: Cerberus, the Hydra, the Chimaera and the Sphinx (305-334)

Men say that Typhaon the terrible, outrageous and lawless, was joined in love to her, the maid with glancing eyes. So she conceived and brought forth fierce offspring; first she bore Orthus the hound of Geryones, and then again she bore a second, a monster not to be overcome and that may not be described, Cerberus who eats raw flesh, the brazen-voiced hound of Hades, fifty-headed, relentless and strong. And again she bore a third, the evil-minded Hydra of Lerna, whom the goddess, white-armed Hera nourished, being angry beyond measure with the mighty Heracles. And her Heracles, the son of Zeus, of the house of Amphitryon, together with warlike Iolaus, destroyed with the unpitying sword through the plans of Athena the spoil driver. She was the mother of Chimaera who breathed raging fire, a creature fearful, great, swift footed and strong, who had three heads, one of a grim-eyed lion, another of a goat, and another of a snake, a fierce dragon; in her forepart she was a lion; in her hinderpart, a dragon; and in her middle, a goat, breathing forth a fearful blast of blazing fire. Her did Pegasus and noble Bellerophon slay; but Echidna was subject in love to Orthus and brought forth the deadly Sphinx which destroyed the Cadmeans, and the Nemean lion, which Hera, the good wife of Zeus, brought up and made to haunt the hills of Nemea, a plague to men. There he preyed upon the tribes of her own people and had power over Tretus of Nemea and Apesas: yet the strength of stout Heracles overcame him. And Ceto was joined in love to Phorcys and bore her youngest, the awful snake who guards the apples all of gold in the secret places of the dark earth at its great bounds.