Laudator Temporis Acti

Theognis 815-816 (tr. J.M. Edmonds):

An ox that setteth his strong hoof upon my tongue restraineth me from blabbing albeit I know.

βοῦς μοι ἐπὶ γλώσσῃ κρατερῷ ποδὶ λὰξ ἐπιβαίνων
   ἴσχει κωτίλλειν καίπερ ἐπιστάμενον.

Aeschylus, Agamemnon 36-39 (tr. Herbert Weir Smyth):

For the rest I'm dumb; a great ox stands upon my tongue—yet the house itself, could it but speak, might tell a tale full plain; since, for my part, of mine own choice I have words for such as know, and to those who know not I've lost my memory.

τὰ δ' ἀλλὰ σιγῶ· βοῦς ἐπὶ γλώσσῃ μέγας
βέβηκεν· οἶκος δ' αὐτός, εἰ φθογγὴν λάβοι,
σαφέστατ' ἂν λέξειεν· ὡς ἑκὼν ἐγὼ
μαθοῦσιν αὐδῶ κοὐ μαθοῦσι λήθομαι.

Strattis, fragment 72 Kassel-Austin = 67 Kock (tr. J.M. Edmonds):

A great ox treads upon (me).

βοῦς ἐμβαίνει μέγας.

Philostratus, Life of Apollonius of Tyana 6.11.27 (talking about Pythagoras; tr. F.C. Conybeare):

[H]e was the first of mankind to restrain his tongue, inventing a discipline of silence described in the proverbial phrase, "An ox sits upon it."

γλῶττάν τε ὡς πρῶτος ἀνθρώπων ξυνέσχε βοῦν ἐπ᾽ αὐτῇ σιωπῆς εὑρὼν δόγμα.

Julian, Orations 7.217d-218a (tr. Wilmer Cave Wright):

But I was impelled I know not how to rave with his own sacred frenzy when I spoke like this of the attributes of great Dionysus; and now I set an ox on my tongue: for I may not reveal what is too sacred for speech.

ἀλλὰ ταῦτα ὲν ἀμφὶ τὸν μέγαν Διόνυσον οὐκ οἶδ' ὅπως ἐπῆλθέ μοι βακχεύοντι μανῆναι· τὸν βοῦν ἐπιτίθημι τῇ γλώττῃ· περὶ τῶν ἀρρήτων γὰρ οὐδὲν χρὴ λέγειν.

Synesius, Letters 154 (tr. Augustus Fitzgerald):

These are the two types of men who have falsely accused me with occupying myself in trivial pursuits, one of them because I do not talk the same sort of nonsense as they do, the other because I do not keep my mouth shut, and do not keep the 'bull on my tongue', as they do.

ἄμφω με τούτω τὼ γένη διαβεβλήκατον, ὡς ἐπὶ τοῖς οὐδενὸς ἀξίοις ἐσπουδα κότα· τὸ μὲν ὅτι μὴ ταὐτὰ φλυαρῶ, τὸ δὲ ὅτι μὴ τὸ στόμα συγκλείσας ἔχω καὶ βοῦν τὸν ἐκείνων ἐπὶ τῆς γλώττης τίθεμαι.

Suda β 460 Adler (tr. Catherine Roth):

An ox on the tongue: [sc. A proverbial phrase] in reference to those who are not able to speak freely: either because of the strength of the animal, or because there was an ox stamped on the Athenian coin which those who spoke freely had to pay.

βοῦς ἐπὶ γλώττης· ἐπὶ τῶν μὴ δυναμένων παρρησιάζεσθαι· ἢ διὰ τὴν ἰσχὺν τοῦ ζῴου. ἢ διὰ τὸ τῶν Ἀθηναίων νόμισμα βοῦν ἔχειν ἐγκεχαραγμένον, ὅπερ ἐκτίνειν ἔδει τοὺς παρρησιαζομένους.