Steve Ray has a list of 35 loaded Questions for "Bible Christians" (quotation marks his)(link to the whole list). This is number 13/35. I'm trying to provide the answers in a common format, for easy reference.
13) Where does the Bible claim to be the sole authority for Christians in matters of faith and morals?
Nowhere that we know of.
1) The reason for the "nowhere" answer is the misleading/loaded wording of the question. There was a similar problem with the first question (1) Where did Jesus give instructions that the Christian faith should be based exclusively on a book?). These are questions like the question asked in the garden by the serpent about the prohibition on eating fruit.
2) The Holy Spirit, after all, is an authority for Christian in matters of faith and morals, and the Holy Spirit speaks not only through the Scripture but also through general revelation and the conscience.
3) Additionally, while they are not infallible authorities, the church are nevertheless authorities.