###Answer the question from the input provided. Please answer from input only.

###Input: In 1516, Johann Tetzel, a Dominican friar and papal commissioner for indulgences, was sent to Germany by the Roman Catholic Church to sell indulgences to raise money to rebuild St. Peter's Basilica in Rome. Roman Catholic theology stated that faith alone, whether fiduciary or dogmatic, cannot justify man; justification rather depends only on such faith as is active in charity and good works (fides caritate formata). The benefits of good works could be obtained by donating money to the church.

On 31 October 1517, Luther wrote to his bishop, Albert of Mainz, protesting the sale of indulgences. He enclosed in his letter a copy of his "Disputation of Martin Luther on the Power and Efficacy of Indulgences", which came to be known as The Ninety-Five Theses. Hans Hillerbrand writes that Luther had no intention of confronting the church, but saw his disputation as a scholarly objection to church practices, and the tone of the writing is accordingly "searching, rather than doctrinaire." Hillerbrand writes that there is nevertheless an undercurrent of challenge in several of the theses, particularly in Thesis 86, which asks: "Why does the pope, whose wealth today is greater than the wealth of the richest Crassus, build the basilica of St. Peter with the money of poor believers rather than with his own money?"

Luther objected to a saying attributed to Johann Tetzel that "As soon as the coin in the coffer rings, the soul from purgatory (also attested as 'into heaven') springs."

He insisted that, since forgiveness was God's alone to grant, those who claimed that indulgences absolved buyers from all punishments and granted them salvation were in error. Christians, he said, must not slacken in following Christ on account of such false assurances.

However, this oft-quoted saying of Tetzel was by no means representative of contemporary Catholic teaching on indulgences, but rather a reflection of his capacity to exaggerate. Yet if Tetzel overstated the matter in regard to indulgences for the dead, his teaching on indulgences for the living was in line with Catholic dogma of the time.



###Question: When did Martin Luther protest the sale of indulgences to his bishop?

###Answer: {'answer':'31 October 1517'}