Passage 1.35.1
νῆσοι δὲ Ἀθηναίοις οὐ πόρρω τῆς χώρας εἰσίν, ἡ μὲν Πατρόκλου καλουμένη---τὰ δὲ ἐς αὐτὴν ἤδη μοι δεδήλωται---, ἄλλη δὲ ὑπὲρ Σουνίου τὴν Ἀττικὴν ἐν ἀριστερᾷ παρα πλέουσιν· ἐς ταύτην ἀποβῆναι λέγουσιν Ἑλένην μετὰ τὴν ἅλωσιν τὴν Ἰλίου, καὶ διὰ τοῦτο ὄνομά ἐστιν Ἑλένη τῇ νήσῳ.
Not far from Attica lie certain islands belonging to the Athenians, one of which is called Patroclus' Island—I have already described what pertains to this one. Another lies off Attica beyond Sounion, on the left as you sail past. They say that after the capture of Ilium, Helen landed upon this island, and for this reason the island bears the name Helen.