If you can read Greek, this is what st. Theodore the Studite writes:
«Ἡ δέ γε τοῦ Αὐγούστου νηστεία εἰς τιμὴν ὑπάρχει τῆς τοῦ Θεοῦ Λόγου Μητρός, ἥτις προγνοῦσα τὴν μετάστασιν ἑαυτῆς, καὶ πάντοτε μὲν ἦν ἀγωνιζομένη ὑπὲρ ἡμῶν νηστεύουσα, μὴ χρείαν ἔχουσα νηστείας ἡ καθαρὰ καὶ πανάμωμος. Διὸ καὶ ἡμεῖς τότε νηστεύειν καὶ ἀνυμνεῖν αὐτὴν ὀφείλομεν, τόν τε βίον αὐτῆς ἐκμιμούμενοι καὶ εἰς τὰς ὑπὲρ ἡμῶν διεγείροντες ἱκεσίας»
[He roughly states that the Dormition fast exists to honour and imitate the Mother of God, who had foreknowlege of her passing and fasted before her Dormition].
St Nicodemus the Hagiorite writes:
«Ὅθεν φέρωντες εἰς τοῦτο καὶ ἄλλας ἀποδείξεις, στοχαστικώτατα ἔφερε καὶ τὸν τόμον τῆς Ἑνώσεως, ὅπου ἔγινεν, ὡς εἴπομεν, εἰς τοὺς 922, εἰς τὸν ὁποῖον βλέπομεν, πῶς οἱ Πατέρες ἐκείνης τῆς Συνόδου ἀναφέρουν κοντὰ εἰς τὴν ἁγίαν Τεσσαρακοστὴν καὶ τὰς ἄλλας δύω, ὅθεν συμπεραίνεται καὶ ἐκεῖθεν ἡ αὐτῶν ἀρχαιότης. Καὶ ἀληθινά, διὰ νὰ εἰποῦμεν καὶ ἡμεῖς ὡς ἐν παρόδῳ πρέπει νὰ ἔχουν καὶ αὐταῖς τὸ αἰδέσιμον, διὰ τί, ὅταν εἰς τὰ 922 ἔτη σημειώνονται, καὶ ἡμεῖς τώρα εὑρισκόμεθα εἰς τοὺς 1790 καὶ ἐπέκεινα, πῶς ἠμποροῦμεν νὰ τὰς λέγωμεν νεωτερίσματα; ἔπειτα τότε σημειώνωνται, μὰ ἀπὸ τότε δὲν ἄρχισαν, ἀλλὰ καὶ προτήτερα ἦσαν, ἤγουν ἐξ ἀρχαίων χρόνων ἐσυνειθίζοντο εἰς τὴν Ἐκκλησίαν, εἶχε διαμορφωθῆ ἤδη κατὰ τὸν Η' αἰῶνα»
[He roughly describes the Dormition Fast as an old one, because it's mentioned for the first time in 922 AD (3rd canon of the local synod of Neocaesarea, in 922 AD) therefore it is a much older custom, probably established in the 8th century]
What is your source for this? What book did you copy this from?
