It was narrated that Humaid bin 'Abdur-Rahman bin 'Awf said:"I heard Mu'awiyah say on the day of 'Ashura when he was on the Mindar: O people of Al-Madinah, where are your scholars? I heard the Messenger of Allah say on this day: "I am fasting, so whoever wants to fast let him do so

English translation · Sunan an-Nasa'i