Canon 18
That the existing prayers for both Vespers and the ninth hour are quite sufficient, and therefore no one has the right to compose new prayers and read them in church.
That the prayer service both at the ninth hour and at Vespers should always be the same.
Greek original
Περὶ τοῦ τὴν αὐτὴν λειτουργίαν τῶν εὐχῶν πάντοτε καὶ ἐν ταῖς ἐννάταις, καὶ ἐν ταῖς ἐσπέραις ὀφείλειν γίνεσθαι.
Parallel canons
Лаод.1559Карф.103