I have found 2 Timothy 3:16 and 17 work for me... "All scripture [is] given by inspiration of God, and [is] profitable for doctrine, for reproof, for correction, for instruction in righteousness: (17) That the man of God may be perfect (COMPLETE), thoroughly furnished unto all good works."
The word of God is what is needed for 1) Doctrine - that which is taught/instructed; 2) Reproof - to prove or test things; 3) Correction - To bring back to an upright state; 3) Instructions in Righteousness - Being taught what is right...
And it's God's Word that makes you complete and thoroughly furnishes (literally perfectly finishes) you for ALL good works.
I have found 2 Timothy 3:16 and 17 work for me... "All scripture [is] given by inspiration of God, and [is] profitable for doctrine, for reproof, for correction, for instruction in righteousness: (17) That the man of God may be perfect (COMPLETE), thoroughly furnished unto all good works."
What does that say about sola scriptura? Saying that "all scripture" is inspired and authoritative doesn't mean that "only scripture" is. And St. Paul himself contradicts your interpretation when he instructs believers to "hold the traditions which you have learned, whether by word, or by our epistle." Interestingly, Catholics have never doubted the authority of "all scriptures" as St. Paul insists in your quoted verse. Rather, it is the Protestants who have rejected the inspiration of some of the scriptures.
This is the biggest problem with sola scriptura in my opinion. Without an inspired table of contents you will always fall back to something extra-scriptural. No matter what you say or do, you have to depend on some form of tradition not contained in the scriptures in order to achieve the most simple task of knowing what is scripture in the first place.
The immediately preceding verse describes the Scriptures as something Timothy has "known from [his] infancy". That didn't include the New Testament, which hadn't been written yet. If 2 Tm 3:16-17 proves that only Scripture is needed, it necessarily proves that only the Old Testament is needed.
BTW, the Greek says pasa graphe, which can just as easily be translated "every Scripture" as "all Scripture".
And it's God's Word that makes you complete and thoroughly furnishes (literally perfectly finishes) you for ALL good works.
Certainly it's necessary, but the problem is that it doesn't say that that's all you need. And it's clearly not all Timothy had, either: he had the church, the "pillar and ground of the truth" (1 Tm 3:15), of which he was not only a member, but a bishop. He had the preaching of Paul (2 Tm 2:2) and the graces conferred on him by his ordination (1 Tm 4:14).