question #1 Sahih Muslim 1129a, Book 13, Hadith 159 : What is the significance of the day of ‘Ashura in Islamic tradition?

People of Medina, where are your scholars? I heard the Messenger of Allah (ﷺ) say on this very day: It is the day of ‘Ashura. Allah has not made fasting on This day obligatory for you but I am fasting. He who likes to observe fast among you should do so, and he who likes not to observe it may not observe it.