Athenaeus, Sophists at Dinner 6.261d-e
Τιρυνθίους δέ φησι Θεόφραστος ἐν τῷ περὶ κωμῳδίας φιλόγελως ὄντας, ἀχρείους δὲ πρὸς τὰ σπουδαιότερα τῶν πραγμάτων καταφυγεῖν ἐπὶ τὸ ἐν Δελφοῖς μαντεῖον ἀπαλλαγῆναι βουλομένους τοῦ πάθους, καὶ τὸν θεὸν ἀνελεῖν αὐτοῖς, ἢν θύοντες τῷ Ποσειδῶνι ταῦρον ἀγελαστὶ τοῦτον ἐμβάλωσιν εἰς τὴν θάλατταν, παύσεσθαι. οἳ δὲ δεδιότες μὴ διαμάρτωσι τοῦ λογίου τοὺς παῖδας ἐκώλυσαν παρεῖναι τῇ θυσίᾳ. μαθὼν οὖν εἷς καὶ συγκαταμιχθείς, ἐπείπερ ἐβόων ἀπελαύνοντες αὐτόν, “τί δῆτ’;” ἔφη· “δεδοίκατε μὴ τὸ σφάγιον ὑμῶν ἀνατρέψω;” γελασάντων δὲ ἔμαθον ἔργῳ τὸν θεὸν δείξαντα ὡς ἄρα τὸ πολυχρόνιον ἦθος ἀμήχανόν ἐστι θεραπευθῆναι.
Theophrastus says, in his book On Comedy, that the people of Tiryns were fond of laughter and that they were no use in more serious matters; wishing to rid themselves of this unfortunate problem, they appealed to the oracle at Delphi, and the god gave them the answer that the problem would stop if they sacrificed a bull to Poseidon, by casting it into the sea, without laughing. They were afraid that they might fail to fulfill the oracle, so they forbade their children to be present at the sacrifice. But one boy found out what was happening and mingled with the crowd. Just as they were shouting at him and driving him away he said, ‘What’s the matter? Are you afraid I’ll upset your victim?’ They laughed, and found out in actual fact that the god had been showing them how it is impossible to cure a disposition of long standing.
= Theophrastus fr. 124 Wimmer.