Passage 5.11.6
Ἱπποδάμειά τε ἡ Οἰνομάου σὺν τῇ μητρὶ καὶ Προμηθεὺς ἔτι ἐχόμενος μὲν ὑπὸ τῶν δεσμῶν, Ἡρακλῆς δὲ ἐς αὐτὸν ἦρται· λέγεται γὰρ δὴ καὶ τόδε ἐς τὸν Ἡρακλέα, ὡς ἀποκτείναι μὲν τὸν ἀετὸν ὃς ἐν τῷ Καυκάσῳ τὸν Προμηθέα ἐλύπει, ἐξέλοιτο δὲ καὶ αὐτὸν Προμηθέα ἐκ τῶν δεσμῶν. τελευταῖα δὲ ἐν τῇ γραφῇ Πενθεσίλειά τε ἀφιεῖσα τὴν ψυχὴν καὶ Ἀχιλλεὺς ἀνέχων ἐστὶν αὐτήν· καὶ Ἑσπερίδες δύο φέρουσι τὰ μῆλα ὧν ἐπιτετράφθαι λέγονται τὴν φρουράν. Πάναινος μὲν δὴ οὗτος ἀδελφός τε ἦν Φειδίου καὶ αὐτοῦ καὶ Ἀθήνῃσιν ἐν Ποικίλῃ τὸ Μαραθῶνι ἔργον ἐστὶ γεγραμμένον.
Hippodameia, daughter of Oinomaos, with her mother, and Prometheus still bound in chains are represented, and Herakles is depicted approaching him. For indeed it is also said of Herakles that he slew the eagle which tormented Prometheus in the Caucasus, and freed Prometheus himself from his chains. Lastly, the painting shows Penthesileia breathing her last and Achilles supporting her. Two of the Hesperides are bearing the apples whose guarding is said to have been entrusted to them. This painting was by Panaenos, who was the brother of Pheidias, who himself painted the Battle of Marathon in the 'Poikile' (Painted) Colonnade at Athens.