The procession of the Spirit according to Marcellus

"Either the Spirit proceeds (ἐκπορευόμενον) from the Father and, therefore, has no need of the ministry of the Son, in that everything that proceeds from the Father must of necessity be perfect, and absolutely cannot need the help of another; or else if [the Spirit] takes from the Son (cf. John 16:14) and depends on His [of the Son] power, then He [the Spirit] no longer proceeds from the Father." (tr. Maspero)

ἢ τὸ πνεῦμα ἐκ τοῦ πατρὸς ἐκπορευόμενον μὴ δεῖσθαι τῆς παρὰ τοῦ υἱοῦ διακονίας (πᾶν γὰρ τὸ ἐκ πατρὸς ἐκπορευόμενον τέλειον εἶναι ἀνάγκη, μηδαμῶς προσδεόμενον τῆς παρ’ ἑτέρου βοηθείας), ἤ, εἰ παρὰ τοῦ υἱοῦ λαμβάνοι καὶ ἐκ τῆς ἐκείνου δυνάμεως διακονοίη τὴν χάριν, μηκέτι ἐκ τοῦ πατρὸς ἐκπορεύεσθαι (Eusebius, Ecclesiastica Theologia, 3.4.4.3–8 [GCS 14:158]).

"He was ever being partaken, but not partaking"

"He was ever being partaken, but not partaking; perfecting, not being perfected; sanctifying, not being sanctified; deifying, not being deified; Himself ever the same with Himself, and with Those with Whom He is ranged; invisible, eternal, incomprehensible, unchangeable, without quality, without quantity, without form, impalpable, self-moving, eternally moving, with free-will, self-powerful, All-powerful (even though all that is of the Spirit is referable to the First Cause, just as is all that is of the Only-begotten); Life and Lifegiver; Light and Lightgiver; absolute Good, and Spring of Goodness; the Right, the Princely Spirit; the Lord, the Sender, the Separator; Builder of His own Temple; leading, working as He wills; distributing His own Gifts; the Spirit of Adoption, of Truth, of Wisdom, of Understanding, of Knowledge, of Godliness, of Counsel, of Fear (which are ascribed to Him) by Whom the Father is known and the Son is glorified; and by Whom alone He is known; one class, one service, worship, power, perfection, sanctification. Why make a long discourse of it?" (Gregory of Nazianzus, On Pentecost, NPNF 2,7, p. 761)