To paraphrase Matthew Barrett’s article, found here- http://thegospelcoalition.org/blogs/tgc/2013/10/31/sola-scriptura-radicalized-and-abandoned/, the following is some brief context and a marvelous quote from Luther.
After debate with Catholic debater Johann Eck over the foremost authority in the Church (in Leipzig, AD 1519), Eck returned to Rome to tell the pope of his findings. Luther was labeled a heretic, along with John Wycliffe and Jan Hus. Luther left the debate further convinced that Scripture, not the pope, was the sole and infallible authority. In 1521, at Worms, Luther was told he must recant. He thought about it for a day and returned, declaring the principle of sola scriptura. He said,
“Unless I am convinced by the testimony of the Scriptures or by clear reason, for I do not trust either in the pope or in councils alone, since it is well known that they often err and contradict themselves, I am bound to the Scriptures I have quoted and my conscience is captive to the Word of God. I cannot and I will not retract anything, since it is neither safe nor right to go against conscience. I cannot do otherwise. Here I stand. May God help me. Amen.”
To read the full article or see Barrett’s citations, click the link found above.