Does the phrase "God the Son" appear in manuscripts or early translations (Textus Receptus, Vulgate, etc.) of the New Testament scriptures? If not, when did the phrase enter into the Christian vernacular?
This question is complicated, of course, by the fact that we must work with translations of the original texts in order to find this wording. However, at least three second-century authors use this phrasing when translated into English: Justin Martyr, Athenagoras of Athens, and Clement of Alexandria.
Justin Martyr (100–165) writes, in Dialogue with Trypho:
And that Christ being Lord, and God the Son of God, and appearing formerly in power as Man, and Angel, and in the glory of fire as at the bush, so also was manifested at the judgment executed on Sodom, has been demonstrated fully by what has been said.1
Καὶ ὅτι κύριος ὢν ὁ Χριστός, καὶ θεὸς θεοῦ υἱὸς ὑπάρχων, καὶ δυνάμει φαινόμενος πρότερον ὡς ἀνὴρ καὶ ἄγγελος, καὶ ἐν πυρὸς δόξῃ, ὡς ἐν τῇ βάτῳ, πέφανται καὶ ἐπὶ τῆς κρίσεως τῆς γεγενημένης ἐπὶ Σόδομα, ἀποδέδεικται ἐν πολλοῖς τοῖς εἰρημένοις.
At least one translation of Athenagoras's Plea for the Christians (~177) includes the specified phrasing, but see the note for an alternative translation:
Who, then, would not be astonished to hear men who speak of God the Father, and of God the Son, and of the Holy Spirit, and who declare both their power in union and their distinction in order, called atheists?2
τίς οὖν οὐκ ἂν ἀπορήσαι τοὺς ἄγοντας θεὸν πατέρα καὶ υἱὸν θεὸν καὶ πνεῦμα ἅγιον, δεικνύντας αὐτῶν καὶ τὴν ἐν τῇ ἑνώσει δύναμιν καὶ τὴν ἐν τῇ τάξει διαίρεσιν, ἀκούσας ἀθέους καλουμένους
Clement of Alexandria (150–215) writes in Salvation of the Rich Man:
They rave about the carcase, which they despise as weak, being blind to the wealth within; knowing not what a “treasure in an earthen vessel” we bear, protected as it is by the power of God the Father, and the blood of God the Son, and the dew of the Holy Spirit.3
καὶ μαίνονται περὶ τὸ σαρκίον, οὗ καταφρονοῦσιν ὡς ἀσθενοῦς, τῶν ἔνδον ὄντες τυφλοὶ κτημάτων, οὐκ ἐπιστάμενοι πηλίκον τινὰ "θη σαυρὸν ἐν ὀστρακίνῳ σκεύει" βαστάζομεν, δυνάμει θεοῦ πατρὸς καὶ αἵματι θεοῦ παιδὸς καὶ δρόσῳ πνεύματος ἁγίου περιτετειχισμένον.
I'm unable to find this phrasing in the earliest fathers, like Polycarp or Ignatius, suggesting that the middle of the 2nd century is the earliest such record available to us.
- Dialogue with Trypho, chapter 128, in Ante-Nicene Fathers. "God the Son" also appears in a modern translation, published 2003, in Selections from the Fathers of the Church.
- A Plea for the Christians, chapter 10, in Ante-Nicene Fathers. In a 1956 translation, the phrasing is "Who then would not be amazed hearing those called atheists who call God Father and Son and Holy Spirit...?"
- Salvation of the Rich Man, chapter 34, in Ante-Nicene Fathers. The same language is used in Butterworth's 1919 translation.
From the opening of Ignatius' Letter to the Smyrneans:
I glorify Jesus Christ, the God who made you so wise, for I observed that you are established in an unshakable faith, having been nailed, as it were, to the cross of the Lord Jesus Christ in both body and spirit and firmly established in love by the blood of Christ totally convinced with regard to our Lord that he is truly of the family of David with respect to human descent, Son of God with respect to the divine will and power, truly born of a virgin, baptized by John in order that all righteousness might be fulfilled by him, truly nailed in the flesh for us under Pontius Pilate and Herod the tetrarch (from its fruit we derive our existence that is, from his divinely blessed suffering), in order that he might raise a banner for the ages through his resurrection for his saints and faithful people, whether among Jews or among Gentiles, in the one body of his church.
I added the emphasis to make the phrase easier to find. The quotation is from The Apostolic Fathers: Greek texts and English translations, edited and revised by Michael W. Holmes. This establishes the use of the phrase at the beginning of the second century.