Theodoret of Cyrrhus (393-466) commentary on 2 Timothy 3:15-4:2:
"And the fact that from a child you have known the sacred writings, which are capable of instructing you for salvation through faith in Christ Jesus (v. 15). And since he had borne further witness to the extent of the power in the sacred writings, he emphasizes as well the benefit stemming from them. All Scripture is divinely-inspired and of benefit (v.16). Making a distinction, he sets the writings apart from the works of human wisdom, referring to the spiritual Scripture as divinely-inspired: the grace of the divine Spirit spoke through the inspired authors of Old and New Testaments. It follows that the Holy Spirit is God if the Spirit’s Scripture is, as the apostle says, divinely-inspired. He brings out the kinds of benefit. For teaching: what we did not know we learned from there. For censure: it censures our lawless life. For correction: it urges the backsliders to return to the straight and narrow. For training in righteousness: it drills us in the forms of virtue. So that whoever belongs to God may be well prepared, equipped for every good work (v.17). All these virtues bring about perfection and relate us to the God of all. Having thus brought out the benefit of the divinely-inspired Scripture, he bids him make it available to everyone, and instills dread by his adjuration. I adjure you, therefore, in the presence of God and of the Lord Jesus Christ, who is due to judge living and dead: in view of his coming and kingdom, preach the word (4:1-2)."
Source: Robert Charles Hill, trans., Theodoret of Cyrus: Commentary on the Letters of St. Paul, Vol. 2 (Brookline: Holy Cross Orthodox Press, 2001), pp. 245-246..
For an excellent compilation of quotes of the Church fathers teaching on the primacy, sufficiency and ultimate authority of Scripture, get a copy of Holy Scripture:The Ground and Pillar of Our Faith Vol III- The Writings of the Church Fathers Affirming the Reformation Principle of Sola Scriptura.