When the "reformers" split from the Church Christ directly founded setting the Apostles and their successors as its leaders and giving them His full oral tradition, there was a problem.
Obviously THAT Church could no longer be authoritative for those who left it. So by necessity, they made the very UN-biblical claim that the Bible alone was their only rule of faith. (Ironic as neither Christ nor the Bible make such an assertion and given that the Bible itself is the fruit of Catholic Sacred Tradition.)
This led to the Protestant polemic asking "where is that in the Bible"? Most of the time, that question (based in an invalid supposition as it is), CAN be answered if not with direct citations, then indirect ones.
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