Canon 31
On the prohibition of entering into mixed marriages with people of other faiths, except in cases where the person of other faiths makes a promise to accept the Orthodox faith.
That one should not enter into marriage with any (πάντας) heretics or give them sons or daughters, but it is better to take from them themselves, if only they promise to become Christians.
Greek original
Ὅτι οὐ δεῖ πρὸς πάντας αἱρετικοὺς ἐπιγαμίας ποιεῖν, ἤ διδόναι υἱούς, ἢ θυγατέρας, ἀλλὰ μᾶλλον λαμβάνειν, εἴγε ἐπαγγέλοιντο Χριστιανοὶ γίνεσθαι.
Parallel canons
Ап.264565IVВс.14Трул.672Лаод.10Карф.21