Hilary of Poitiers
“Concerning the Holy Spirit . . . it is not necessary to speak of him who must be acknowledged, who is from the Father and the Son, his sources” (
The Trinity 2:29 [A.D. 357]).
“In the fact that before times eternal your [the Father’s] only-begotten [Son] was born of you, when we put an end to every ambiguity of words and difficulty of understanding, there remains only this: he was born. So too, even if I do not g.asp it in my understanding, I hold fast in my consciousness to the fact that your Holy Spirit is from you through him” (
ibid., 12:56).
Didymus the Blind
“As we have understood discussions . . . about the incorporeal natures, so too it is now to be recognized that the Holy Spirit receives from the Son that which he was of his own nature. . . . So too the Son is said to receive from the Father the very things by which he subsists. For neither has the Son anything else except those things given him by the Father, nor has the Holy Spirit any other substance than that given him by the Son” (
The Holy Spirit 37 [A.D. 362]).
**Epiphanius of Salamis
**
“The Father always existed and the Son always existed, and the Spirit breathes from the Father and the Son” (
The Man Well-Anchored 75 [A.D. 374]).
Basil The Great
“[T]he goodness of [the divine] nature, the holiness of [that] nature, and the royal dignity reach from the Father through the only-begotten [Son] to the Holy Spirit. Since we confess the persons in this manner, there is no infringing upon the holy dogma of the monarchy” (
The Holy Spirit, 18:47).
“Even if the Holy Spirit is third in dignity and order, why need He be third also in nature? For that He is second to the Son, having His being from Him and receiving from Him and announcing to us and being completely dependent on Him, pious tradition recounts; but that His nature is third we are not taught by the Saints nor can we conclude logically from what has been said” (
Against Eunomius 3:1)
Ambrose of Milan
“Just as the Father is the fount of life, so too, there are many who have stated that the Son is designated as the fount of life. It is said, for example that with you, Almighty God, your Son is the fount of life, that is, the fount of the Holy Spirit. For the Spirit is life, just as the Lord says: ‘The words which I have spoken to you are Spirit and life’ [John 6:63]” (
The Holy Spirit 1:15:152 [A.D. 381]).
“The Holy Spirit, when he proceeds from the Father and the Son, does not separate himself from the Father and does not separate himself from the Son” (
ibid., 1:2:120).
Gregory of Nyssa
“[The] Father conveys the notion of unoriginate, unbegotten, and Father always; the only-begotten Son is understood along with the Father, coming from him but inseparably joined to him. Through the Son and with the Father, immediately and before any vague and unfounded concept interposes between them, the Holy Spirit is also perceived conjointly” (
Against Eunomius 1 [A.D. 382]).
Cyril of Alexandria
“Since the Holy Spirit when he is in us effects our being conformed to God, and he actually proceeds from the Father and Son, it is abundantly clear that he is of the divine essence, in it in essence and proceeding from it” (
Treasury of the Holy Trinity, thesis 34 [A.D. 424]).
“[T]he Holy Spirit flows from the Father in the Son” (
ibid.).
Pope Leo the Great
“Thus, in the first chapter it is shown what impious notions they hold concerning the divine Trinity, when they assert that there is one and the same person of the Father and the Son and the Holy Spirit, as though the same God should at one time be named Father, at another time Son, at another time Holy Spirit; and as though there were not one Who begat, another Who is begotten, another Who proceeds from both.” (
Letter to Bishop St. Turibius of Astorga 15:2)
John Damascene
“Likewise we believe also in one Holy Spirit, the Lord and giver of life . . . God existing and addressed along with Father and Son; uncreated, full, creative, all-ruling, all-effecting, all-powerful, of infinite power, Lord of all creation and not under any lord; deifying, not deified; filling, not filled; sharing in, not shared in; sanctifying, not sanctified; the intercessor, receiving the supplications of all; in all things like to the Father and Son; proceeding from the Father and communicated through the Son” (
Exposition of the Orthodox Faith 8 [A.D. 712]).
“And the Holy Spirit is the power of the Father revealing the hidden mysteries of his divinity, proceeding from the Father through the Son in a manner known to himself, but different from that of generation” (
ibid., 12).
“I say that God is always Father since he has always his Word [the Son] coming from himself and, through his Word, the Spirit issuing from him” (
Dialogue Against the Manicheans 5 [A.D. 728]).
All these seem pretty explicit to me, though I am nobody.