Sunan An-Nasa'i

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