question #3 Sahih Muslim 1126d, Book 13, Hadith 151 : What is the stance on voluntary fasting on the day of Ashura according to Islamic teachings?

It is a day on which the people of pre-Islamic days observed fast. So he who liked to fast on this day should do so, and he who liked to abandon it should abandon it. ‘Abdullah (Allah be pleased with him) did not observe fast except when it coincided (with the days when he was in the habit of observing voluntary fasts during every month).