"Almighty God, you have given us grace at this time with one accord to make our common supplication to you; and you have promised through your well-beloved Son that when two or three are gathered together in his Name you will be in the midst of them: Fulfill now, O Lord, our desires and petitions as may be best for us; granting us in this world knowledge of your truth, and in the age to come life everlasting. Amen."
A prayer of St. Chrysostom, Morning and Evening Prayer, Book of common prayer (1979). According to Hatchett (pp. 130-131, which see), Cranmer derived this from "the entrance rite of the late medieval manuscripts of the liturgies of Saint John Chrysostom and Saint Basil" (it being absent from "the earliest manuscripts"). Hence (for the Liturgy of St. Chrysostom):
Ὁ τὰς κοινὰς ταύτας καὶ συμφώνους ἡμῖν χαρισάμενος προσευχάς, ὁ καὶ δυσὶ [(δύο in the Liturgy of St. Basil)] καὶ τρισὶ συμφωνοῦσιν ἐπὶ τῷ ὀνόματί σου τὰς αἰτήσεις παρέχειν ἐπαγγειλάμενος· αὐτὸς καὶ νῦν τῶν δούλων σου τὰ αἰτήματα πρὸς τὸ συμφέρον πλήρωσον χορηγῶν ἡμῖν ἐν τῷ παρόντι αἰῶνι τὴν ἐπίγνωσιν τῆς σῆς ἀληθείας καὶ ἐν τῷ μέλλοντι ζωὴν αἰώνιον χαριζόμενος.
Enarxis (Commencement), modern Liturgy of St. Chrysostom, as reproduced in F. E. Brightman, Liturgies, eastern and western (1896), 367, ll. 18-23. Cf. H. A. Daniel, Codex liturgicus ecclesiae universae in epitomen redactus, vol. 4 (1893), 343, and elsewhere. According to Hatchett, this was followed by the doxology on the previous page of Brightman:
Ὅτι ἀγαθὸς καὶ φιλάνθρωπος Θεὸς ὑπάρχεις καὶ σοὶ τὴν δόξαν ἀναπέμπομεν τῷ Πατρὶ καὶ τῷ Υἱῷ καὶ τῷ ἁγίῳ Πνεύματι νῦν καὶ ἀεὶ καὶ εἰς τοὺς αἰῶνας τῶν αἰώνων
For the 8th/9th-century Liturgy of St. Basil, see Brightman 311 l. 22-312, l. 2, and Cod. Vat. Barb. gr. 336, fol. 2v-3r. This (called "The Prayer of the Third Antiphon") is rendered by the Greek Orthodox Archdioese in America as follows:
Priest (in a low voice):Lord, You have granted us to offer these common prayers in unison and have promised that when two or three agree in Your name, You will grant their requests. Fulfill now, O Lord, the petitions of Your servants as may be of benefit to them, granting us in the present age the knowledge of Your truth, and in the age to come eternal life.
And he exclaims:For You, O God, are good and love mankind, and to You we offer glory, to the Father and to the Son and to the Holy Spirit, now and forever and to the ages of ages.My own extremely literal and non-idiomatic little mere crib I supply here:
Thou [who (Ὁ)] art granting [(χαρισάμενος, ADP-NMS)] these common prayers in which we agree; Thou [who (ὁ)] art also promising [(ἐπαγγειλάμενος, AMP-NMS)] to grant [(παρέχειν)] the requests [of the] two and three [who] agree on your name; [the] same will also now be fulfilling [(πλήρωσον, FAP-NMS)] the requests of your servants unto/in order to/for the profitable, furnishing [(χορηγῶν, pAP-NMS)] us in the present aeon [with] the knowledge of thy truth and in the coming aeon life eternal granting [(χαριζόμενος, pAP-NMS)].Latin translation (which, according to Hatchett, misled Cranmer). From Anselm Strittmatter, "'Missa Grecorum' 'Missa Sancti Iohannis Chrisostomi': the oldest Latin version known of the Byzantine liturgies of St. Basil and St. John Chrysostom," Traditio 1 (1943): 92 l. 27-94 l. 2 (79-137). For "ducibus et tribubus" read "duobus et tribus"; on the mistranslation "ad conferendum", see 86 and 86n15; for "impresenti" Strittmatter offers "presenti":
Deus qui has communes et consonas orationes donasti, qui et ducibus et tribubus in nomine tuo conuenientibus peticiones prebere promisisti, ipse nunc postulationes seruorum tuorum ad conferendum comple, in presenti saeculo tuae ueritatis cognitionem largiendo et in futuro nobis uitam aeternam donaturus.
Quoniam obtimus et amator hominum existis, ac tibi gloriam dirigimus, patri et filio et spiritui sancto nunc et semper et in saecula saeculorum amen.
1549: "Letany and Suffrages", The book of the common prayer, as reproduced in Cummings (2011), 45: "Almightie God, whiche hast geven us grace at this tyme | with one accorde to make our commune supplicacions | unto thee, and doest promise, that whan two or three | bee gathered in thy name, thou wylt graunt theyr | requestes: fulfill now, O lorde, the desires | and peticions of thy servauntes, as | maye bee moste expediente for them, | grauntyng us in this worlde know- | lege of thy trueth, and in | the worlde to come | lyfe everlasting. | Amen."
1662: Morning and Evening Prayer, Litany, Book of common prayer, as reproduced in Cummings (2011), 249, 257, 264: "Almighty God, who hast given us grace at this time with one accord to make our common supplications unto thee, and dost promise, that when two or three are gathered together in the Name, though wilt grant their requests; Fulfill now, O Lord, the desires and petitions of thy servants, as may be most expedient for them; granting us in this world knowledge of thy truth, and in the world to come life everlasting. Amen."