"I believe that the Spirit proceeds not otherwise than from the Father through the Son" (Against Praxeas 4:1 [A.D. 216]).
"We believe, however, that there are three persons: the Father and the Son and the Holy Spirit; and we believe none to be unbegotten except the Father. We admit, as more pious and true, that all things were produced through the Word, and that the Holy Spirit is the most excellent and the first in order of all that was produced by the Father through Christ" (Commentaries on John 2:6 [A.D. 229]).
Maximus the Confessor
"By nature the Holy Spirit in his being takes substantially his origin from the Father through the Son who is begotten (Questions to Thalassium 63 [A.D. 254]).
Gregory the Wonderworker
"[There is] one Holy Spirit, having substance from God, and who is manifested through the Son; image of the Son, perfect of the perfect; life, the cause of living; holy fountain; sanctity, the dispenser of sanctification; in whom is manifested God the Father who is above all and in all, and God the Son who is through all. Perfect Trinity, in glory and eternity and sovereignty neither divided nor estranged" (Confession of Faith [A.D. 265]).
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]).
Hilary of Poitiers
"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 grasp 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
"Through the Son, who is one, he [the Holy Spirit] is joined to the Father, one is one, and by himself completes the Blessed Trinity (The Holy Spirit 18:45 [A.D. 375]).
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 6:64]" (The Holy Spirit 1:15:152 [A.D. 381]).
Ambrose of Milan
"The Holy Spirit, when he proceeds from the father and the Son, does not separate himself from the Father and does not separate himself form 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]).
The Athanasian Creed
"[W]e venerate one God in the Trinity and the Trinity in oneness . . . The Father was not made nor created nor begotten by anyone. The Son is from the Father alone, not made nor created, but begotten. The Holy Spirit is from the Father and the Son, not made nor created nor begotten, but proceeding" (Athanasian Creed [A.D. 400]).
"If that which is given has for its principle the one by whom it is given, because it did not receive from anywhere else that which proceeds from the giver, then it must be confessed that the Father and the Son are the principle of the Holy Spirit, not two principles, but just as the Father and the Son are one God . . . relative to the Holy Spirit they are one principle" (The Trinity 5:14:15 [A.D. 408]).
"[The one] from whom principally the Holy Spirit proceeds is called God the Father. I have added the term 'principally' because the Holy Spirit is found to proceed also from the Son" (ibid., 15:17:29).
"Why, then, should we not believe that the Holy Spirit proceeds also from the Son, when he is the Spirit also of the Son? For if the Holy Spirit did not proceed from him, when he showed himself to his disciples after his resurrection he would not have breathed upon them, saying, 'Receive the Holy Spirit' [John 20:22]. For what else did he signify by that breathing upon them except that the Holy Spirit proceeds also from him" (Homilies on John 99:8 [A.D. 416]).
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.).
"The Spirit proceeds (proeisi) from the Father and the Son; clearly, he is of the divine substance, proceeding (proion) substantially (ousiodos) in it and from it" (St. Cyril of Alexandria, Thesaurus, PG 75, 585 A)
"Just as the Son says 'All that the Father has is mine' [John 16:15], so shall we find that through the Son it is all also in the Spirit" (Letters 3:4:33 [A.D. 433]).
Gregory the Great
Gregory the Great taught the Filioque and Photius was aware of this and tried to excuse him (in his Mystagogia); Leo the Great taught the Filioque and wrote to the Spanish Church about the teaching a few years before he wrote his definitive Tome on Christology to the East. (Letter: Quam laudabiliter in 447: DS284).
Council of Toledo
"We believe in one true God, Father and Son and Holy Spirit, maker of the visible and the invisible. . . . The Spirit is also the Paraclete, who is himself neither the Father nor the Son, but proceeding from the Father and the Son. Therefore the Father is unbegotten, the Son is begotten, the Paraclete is not begotten but proceeding from the Father and the Son" (Council of Toledo [A.D. 447]).
Fulgence of Ruspe
"Hold most firmly and never doubt in the least that the only God the Son, who is one person of the Trinity, is the Son of the only God the Father; but the Holy Spirit himself also one person of the Trinity, is Spirit not of the Father only, but of Father and of Son together" (The Rule of Faith 53 [A.D. 524]).
Fulgence of Ruspe
"Hold most firmly and never doubt in the least that the same Holy Spirit who is Spirit of the Father and of the Son, proceeds from the Father and the Son" (ibid., 54).
Maximus the Confessor (650 AD) defends Pope Martin's teaching on the Filioque and answers the very objections of the Greeks. Maximus's response:
"Those of the Queen of cities (Constantinople) have attacked the synodic letter of the present very holy Pope, not in the case of all the chapters that he has written in it, but only in the case of two of them. One relates to the theology (of the Trinity) and, according to them, says: 'The Holy Spirit also has his ekporeusis (ekporeuesthai) from the Son'. The other deals with the divine incarnation. "With regard to the first matter, they (the Romans) have produced unanimous evidence of the Latin Fathers, and also of Cyril of Alexandria, from the study he made of the gospel of St. John. On the basis of these texts, they have shown that they have not made the Son the cause (aitian) of the Spirit - they know in fact that the Father is the only cause of the Son and the Spirit, the one by begetting and the other by ekporeusis (procession) - but that they have manifested the procession through him (to dia autou proienai) and have thus shown the unity and identity of the essence... "They (the Romans) have therefore been accused of precisely those things which it would be wrong to accuse them, whereas the former (the Byzantines) have been accused of those things of which it has been quite correct to accuse them (Monothelitism). They have up till now produced no defence, although they have not yet rejected the things that they have themselves so wrongly introduced. "In accordance with your request, I have asked the Romans to translate what is peculiar to them [the 'also from the son'] in such a way that any obscurities that may result from it will be avoided. But since the practice of writing and sending [the synodic letter] has been observed, I wonder whether they will possibly agree to do this. It is true, of course, that they cannot reproduce their idea in a language and in words that are foreign to them as they can in their mother-tongue, just as we too cannot. In any case, having been accused, they will certainly take some care about this."
"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; shared in, not sharing 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]).
Council of Nicaea II
"We believe in the Holy Spirit, the Lord and giver of life, proceeds from the Father through the Son" (Profession of Faith [A.D. 787]).