Canon 39
About the ban on participating in pagan holidays.
About the fact that one should not celebrate with the pagans and join in their atheism.
Greek original
Ὅτι οὐ δεῖ τοῖς ἔθνεσι συνεορτάζειν, καὶ κοινωνεῖν τῇ ἀθεότητι αὐτῶν.
Parallel canons
Ап.71Трул.7194