Passage 1.32.6
ἔστι δὲ ἐν τῷ Μαραθῶνι πηγὴ καλουμένη Μακαρία, καὶ τοιάδε ἐς αὐτὴν λέγουσιν. Ἡρακλῆς ὡς ἐκ Τίρυνθος ἔφευγεν Εὐρυσθέα, παρὰ Κήυκα φίλον ὄντα μετοικίζεται βασιλεύοντα Τραχῖνος. ἐπεὶ δὲ ἀπελθόντος ἐξ ἀνθρώπων Ἡρακλέους ἐξῄτει τοὺς παῖδας Εὐρυσθεύς, ἐς Ἀθήνας πέμπει σφᾶς ὁ Τραχίνιος ἀσθένειάν τε λέγων τὴν αὑτοῦ καὶ Θησέα οὐκ ἀδύνατον εἶναι τιμωρεῖν· ἀφικόμενοι δὲ οἱ παῖδες ἱκέται πρῶτον τότε Πελοποννησίοις ποιοῦσι πόλεμον πρὸς Ἀθηναίους, Θησέως σφᾶς οὐκ ἐκδόντος αἰτοῦντι Εὐρυσθεῖ. λέγουσι δὲ Ἀθηναίοις γενέσθαι χρησμὸν τῶν παίδων ἀποθανεῖν χρῆναι τῶν Ἡρακλέους τινὰ ἐθελοντήν, ἐπεὶ ἄλλως γε οὐκ εἶναι νίκην σφίσιν· ἐνταῦθα Μακαρία Δηιανείρας καὶ Ἡρακλέους θυγάτηρ ἀποσφάξασα ἑαυτὴν ἔδωκεν Ἀθηναίοις τε κρατῆσαι τῷ πολέμῳ καὶ τῇ πηγῇ τὸ ὄνομα ἀφʼ αὑτῆς.
In Marathon there is a spring called Macaria, and about it they tell the following story. When Heracles was fleeing from Eurystheus out of Tiryns, he settled with his friend Ceyx, who was the king of Trachis. But after the death of Heracles, Eurystheus demanded his children, and the Trachinian, claiming his own weakness and that Theseus would likely be strong enough to defend them, sent them forth to Athens. Upon their arrival as suppliants, the Peloponnesians then for the first time made war against the Athenians, because Theseus refused to give the children over to Eurystheus who demanded them. The Athenians say an oracle was delivered to them, that victory could not otherwise come unless one of Heracles’ children willingly died. At this point Macaria, the daughter of Heracles and Deianeira, slew herself willingly, thus giving victory to the Athenians in battle and naming the spring after herself.