Opponents of sola scriptura seem to think that if it were true, Protestants ought to be able to point to a verse which spells out sola scriptura. But that's a very crude understanding of how the Bible teaches something. The Bible contains implicit as well as explicit teaching.
For instance, even in the OT there was the fundamental dichotomy between true and false prophets. Those who spoke truly for God and those who spoke falsely for God. Well, that's an incipient sola scriptura principle. It just hadn't been written down at that stage.
In Protestant theology, Scripture is to true prophecy as an infallible church is to false prophecy.