Passage 1.41.9
καὶ ὁ μὲν ἐτελεύτησεν ἐν τοῖς Μεγάροις αὐτοχειρίᾳ, καί οἱ τάφον αὐτίκα ἔχωσαν καὶ θύουσιν ἀνὰ πᾶν ἔτος ψηφῖσιν ἐν τῇ θυσίᾳ ἀντὶ οὐλῶν χρώμενοι καὶ τὸν ἔποπα τὸν ὄρνιθα ἐνταῦθα φανῆναι πρῶτον λέγουσιν· αἱ δὲ γυναῖκες ἐς μὲν Ἀθήνας ἀφίκοντο, θρηνοῦσαι δὲ οἷα ἔπαθον καὶ οἷα ἀντέδρασαν ὑπὸ δακρύων διαφθείρονται, καί σφισι τὴν ἐς ἀηδόνα καὶ χελιδόνα μεταβολὴν ἐπεφήμισαν ὅτι οἶμαι καὶ αὗται αἱ ὄρνιθες ἐλεεινὸν καὶ θρήνῳ ὅμοιον ᾄδουσιν.
And he ended his life by his own hand at Megara. Immediately they raised a tomb for him and offer annual sacrifices there, using small pebbles instead of grains during the ritual. They also say the hoopoe bird appeared there for the first time. The women, however, arrived at Athens, but while lamenting their sufferings and deeds, perished from weeping. Because of this, the tale arose of their transformation into the nightingale and the swallow, possibly since these birds likewise sing songs of pity and mournful lamentation.