Canon 54
About the prohibition for Christians to attend weddings at a time when there are performances befitting only pagans.
That clergy or clerics should not watch spectacles at marriages or dinners, but, before the actors enter, get up and leave.
Greek original
Ὅτι οὐ δεῖ ἱερατικοὺς ἢ κληρικούς τινας θεωρίας θεωρεῖν ἐν γάμοις, ἢ δείπνοις, ἀλλά, πρὸ τοῦ εἰσέρχεσθαι τοὺς θυμελικούς, ἐγείρεσθαι αὐτοὺς καὶ ἀναχωρεῖν.
Parallel canons
Трул.24Лаод.53