Simon Magus who is according to Irenaeus the “Father of all Heretics” and the source of Valentinus teaching:

GREEK TEXT: "...Ὁ Πέτρος ἀπεκρίθη· ὁ κύριος ἡμῶν οὔτε θεοὺς εἶναι ἐφθέγξατο παρὰ τὸν κτίσαντα τὰ πάντα οὔτε ἑαυτὸν θεὸν εἶναι ἀνηγόρευσεν, ὑιὸν δὲ θεοῦ τοῦ τὰ πάντα διακοσμήσαντος τὸν εἱπόντα αὐτὸν εὐλόγως ἐμακάρισεν καὶ ὁ Σίμων ἀπεκρίνατο· οὐ δοκεῖ σοι οὖν τὸν ἀπὸ θεὸν εἶναι; καὶ ὁ Πέτρος ἔφη· πῶς τοῦτο εἶναι δύναται, φράσον ἡμῖν, τοῦτο γὰρ ἡμεῖς εἰπεῖν σοι οὐ δυνάμεθα ὃτι μὴ ἡκούσαμεν παρ᾽ αὐτοῦ..." - (FOOTNOTE 247, CHAPTER III. THE COMMON FAITH AND THE BEGINNINGS OF KNOWLEDGE IN GENTILE CHRISTIANITY AS IT WAS BEING DEVELOPED INTO CATHOLICISM. HISTORY OF DOGMA - VOLUME I, by ADOLF HARNACK)

SIMON MAGUS (circa. 3 B.C.E. to 66 C.E. ): “...When Simon heard this, he said: “Since you say that we ought not to believe even the prophet that gives signs and wonders if he say that there is another god, and that you know that he even incurs the penalty of death, therefore your teacher also was with reason cut off for having given signs and wonders.” And Peter answered: “Our Lord neither asserted that there were gods except the Creator of all, NOR DID HE PROCLAIM HIMSELF TO BE GOD, but He with reason pronounced blessed him who called Him the Son of that God who has arranged the universe.” And SIMON answered: “Does it not seem to you, then, THAT HE WHO COMES - FROM GOD - IS GOD?” And Peter said: “Tell us how this is possible; for we cannot affirm this, because we did not hear it from Him...” - (HOMILY XVI: Chapter XV.—Christ Not God, But the Son of God. The Clementine Homilies. By the Rev. Thomas Smith, D.D. In Roberts & Donalsons ANF.)

Valentinius a Gnostic and Christian Apostate hands down Simon Magus concept of “...that which is begotten ( of ) God, - is – God...”

IRENAEUS (circa. 130-200 C.E.): “...Thou hast indeed enjoined upon me, my very dear friend, that I should bring to light the VALENTINIAN doctrines, concealed, as their votaries imagine; that I should exhibit their diversity, and compose a treatise in refutation of them. Therefore have undertaken -- showing that they spring from SIMON, THE FATHER OF ALL HERETICS -- to exhibit both their doctrines and successions, and to set forth arguments against them all...” – (Book III, Preface, Verse 1, Adv Haer Roberts & Donaldsons ANF.)

IRENAEUS (circa. 130-200 C.E.): “...For, prior to Valentinus, those who follow Valentinus had no existence; nor did those from Marcion exist before Marcion; nor, in short, had any of those malignant-minded people, whom I have above enumerated, any being previous to the initiators and inventors of their perversity. For Valentinus ... But the rest, who are called Gnostics, take rise from Meander, SIMON'S DISCIPLE, as I have shown...” - (Book III, Chapter 4, Verse 3, Adv Haer Roberts & Donaldsons ANF.)

GREEK TEXT: “...τὸ γὰρ ἐκ Θεοῦ γεννηθὲν, Θεός ἐστιν...” - (Ap. D. Advers. Haeres. Lib. I. p. 36. Op. Paris, 1639. [SAME TEXT = Book 1. Chapter 1. Section 18. (ed. W. Wigan Harvey) Sancti Irenaei episcopi Lugdunensis libri quinque adversus haereses, vol. 1. Cambridge: Cambridge University Press, 1857].) 

VALENTINIUS (circa. 100 to 160 C.E.): “...therefore said he [=Valentinius]...by way of inference ; FOR THAT WHICH IS BEGOTTEN OF GOD, IS GOD...” - (Page 28 Gnostic interpretation of the Prolouge of St. John's Gospel. Valentinian perversion of the Holy Scriptures characterized. Five books of S. Irenaeus bishop of Lyons, against heresies. Translated by the Rev. John Keble, with the fragments that remain of his other works. Published 1872 by J. Parker in Oxford.)

Now compare this with Irenaeus own BI{2}-nitarian ( TWO-in-one not THREE-in-one ) views :

IRENAEUS (circa. 130-200 C.E.): “...Therefore, the Father is Lord and the Son is Lord, and the Father is God and the Son is God, SINCE HE WHO IS BORN OF GOD IS GOD..." - (Chapter 47. Proof of the Apostolic Preaching. Joseph P. Smith. Ancient Christian Writers, New York: Newman Press, 1952, p. 78)