Musannaf Ibn Abi Shaybah 9618 — Fasting the day of Ashura

Muhammad said: On the day of Ashura, the Prophet (peace and blessings be upon him) said to a man from the tribe of Aslam: "Go to your people and order them to fast this day." The man said: "I think that by the time I reach them they will have had their morning meal." The Prophet (peace and blessings be upon him) said: "Tell whoever has had his morning meal not to eat for the rest of the day, and tell whoever has not had his morning meal to fast."