You didnt answer the question, that is, where in Scripture does it say that Scripture is ones sole source. Maybe there is no verse in all of Scripture where it says that Scripture is ones sole source.
Well, we could start here to get an idea.
Acts 17:11 Now the Bereans were of more noble character than the Thessalonians, for they received the message with great eagerness and examined the Scriptures every day to see if what Paul said was true.
Obviously the “noble” thing to do is check with scripture on even things Paul and Silas were teaching. Then we have the example of Jesus. How many times did Jesus say “it is written” to back up what He was saying? If even Jesus and Paul want what they are saying backed up by scripture you can count on the fact that I’m going to check with scripture to see what some guy in a pointy hat is teaching.