Chapter 65: Prophetic Commentary on the Qur'an (Tafseer of the Prophet (pbuh))
Narrated Ibn 'Umar: Fasting was observed on the day of 'Ashura' (i. e. 10th of Muharram) by the people of the Pre-lslamic
Period. But when (the order of compulsory fasting) in the month of Ramadan was revealed, the
Prophet said, "It is up to one to fast on it (i. e. day of 'Ashura') or not."
Sahih al-Bukhari 4501