We have the remains of an ancient epic called the Thebais that was attributed to ‘Homer’ by multiple sources in antiquity (although most scholars today, following Aristotle, agree that ‘Homer’ = Iliad and Odyssey or something like that). This epic seems to have told the Theban tale from the cursing of Polyneices and Eteocles by Oedipus through the events of the Seven Against Thebes.

“The epic called Thebais was composed about this war. Kallinos, when he comes to mention this epic, says that Homer composed it. Many authors of considerable repute have believed the same thing. And I like this poem especially, after the Iliad and Odyssey at least.”

ἐποιήθη δὲ ἐς τὸν πόλεμον τοῦτον καὶ ἔπη Θηβαΐς• τὰ δὲ ἔπη ταῦτα Καλλῖνος ἀφικόμενος αὐτῶν ἐς μνήμην ἔφησεν ῞Ομηρον τὸν ποιήσαντα εἶναι, Καλλίνῳ δὲ πολλοί τε καὶ ἄξιοι λόγου κατὰ ταὐτὰ ἔγνωσαν• ἐγὼ δὲ τὴν ποίησιν ταύτην μετά γε ᾿Ιλιάδα καὶ τὰ ἔπη τὰ ἐς ᾿Οδυσσέα ἐπαινῶ μάλιστα.
Pausanias, IX 9.5

Fr. 1 (found in The Contest of Homer and Hesiod)

“Goddess, sing of very-thirsty Argos, from where the Leaders [departed for Thebes]”

῎Αργος ἄειδε, θεά, πολυδίψιον, ἔνθεν ἄνακτες

Fr. 2 (Found in Athenaeus’ Deipnosophists)

“Then the god-bred hero, blond Polyneices,
First placed before Oedipus a fine silver platter,
A thing of god-minded Kadmos. And then
He filled a fine golden cup with sweet wine.
But when he noted that lying before him were the
Honored gifts of his own father, a great evil filled his heart.
Quickly he uttered grievous curses against both
Of his own sons—and he did not escape the dread Fury’s notice—
That they would not divide their inheritance in friendship
But that they would both have ceaseless war and battles.”

αὐτὰρ ὁ διογενὴς ἥρως ξανθὸς Πολυνείκης
πρῶτα μὲν Οἰδιπόδηι καλὴν παρέθηκε τράπεζαν
ἀργυρέην Κάδμοιο θεόφρονος• αὐτὰρ ἔπειτα
χρύσεον ἔμπλησεν καλὸν δέπας ἡδέος οἴνου.
αὐτὰρ ὅ γ’ ὡς φράσθη παρακείμενα πατρὸς ἑοῖο
τιμήεντα γέρα, μέγα οἱ κακὸν ἔμπεσε θυμῶι,
αἶψα δὲ παισὶν ἑοῖσιν ἐπ’ ἀμφοτέροισιν ἐπαρὰς
ἀργαλέας ἠρᾶτο• θοὴν δ’ οὐ λάνθαν’ ᾿Ερινύν•
ὡς οὔ οἱ πατρώϊ’ ἐνηέι φιλότητι
δάσσαιντ’, ἀμφοτέροισι δ’ ἀεὶ πόλεμοί τε μάχαι τε

fr.4 (Found in Scholion to Sophocles’ Oedipus at Colonus, 1375)

“When [Oedipus] noticed the cut of meat, he hurled it to the ground and spoke:
‘Alas, my children have sent this as a reproach to me…’
He prayed to King Zeus and the other gods
That they would go to Hades’ home at each other’s hands.

ἰσχίον ὡς ἐνόησε, χαμαὶ βάλεν εἶπέ τε μῦθον•
‘ὤ μοι ἐγώ, παῖδες μέγ’ ὀνειδείοντες ἔπεμψαν …’
*
εὖκτο Διὶ βασιλῆϊ καὶ ἄλλοις ἀθανάτοισι
χερσὶν ὑπ’ ἀλλήλων καταβήμεναι ῎Αιδος εἴσω.