Saint Avitus, in that book which he wrote concerning the Divinity of the Holy Spirit against Gundobad the Arian king, thus declares the procession of the Holy Spirit from the Father and the Son. Concerning the divinity of the Holy Spirit, whom we read to have been neither made, nor begotten, nor created: He is God, God who works all things in all. And in the same place: But all these things one and the same Spirit works, dividing to each as He wills (1 Cor. 12:11). And Peter in the Acts of the Apostles says: Why have you agreed together among yourselves to lie to the Holy Spirit (Acts 5:9)? And afterward: You have not lied to men, but to God (ibid., 4). Likewise in another place: Do you not know that you are the temple of God, and that the Spirit of God dwells in you (1 Cor. 3:16)? And elsewhere:
If anyone does not have the Spirit of God, he does not belong to Him (Rom. 8:9). But we indeed say that the Holy Spirit proceeds from the Son and the Father.