question #1 Sahih Muslim 1135, Book 13, Hadith 174 : What instructions did the Prophet Muhammad (ﷺ) give regarding fasting on the day of ‘Ashura?

Salama b. al-Akwa’ (Allah be pleased with him) reported that the Messenger of Allah (ﷺ) sent a person of the tribe of Aslam on the day of ‘Ashura and commanded him to declare to the people to observe fast in case they had not observed it, and to complete fast till evening if they had taken food