Hadith: The Messenger of Allah (may Allah's peace and blessings be upon him) fasted on the Day of ‘Āshūrā'

عن ابن عباس رضي الله عنهما أن رسول الله صلى الله عليه وسلم صام يوم عاشوراء وأمر بصيامه.
[صحيح] - [متفق عليه]

Ibn ‘Abbās (may Allah be pleased with him) reported: The Messenger of Allah (may Allah's peace and blessings be upon him) fasted on the Day of ‘Āshūrā', and ordered Muslims to fast on it.
[Authentic hadith] - [Narrated by Bukhari & Muslim]

Explanation

Scholars agreed that fasting on the Day of ‘Āshūrā' is an act of Sunnah (recommended) and not obligatory, and they differed regarding its ruling during the early days of Islam when fasting on it was legislated before the fasting of Ramadan was ordained. Was fasting the Day of ‘Āshūrā' at that time obligatory or not? So, considering the correctness of the view that it was obligatory at that time, then its obligation has been abrogated with other authentic Hadīths, such as the following: ‘Ā'ishah (may Allah be pleased with her) reported that Quraysh used to fast on the Day of ‘Āshūrā' in the pre-Islamic times, then the Messenger of Allah (may Allah's peace and blessings be upon him) ordered fasting on it until Ramadan was made obligatory to fast. In another Hadīth, the Messenger of Allah (may Allah's peace and blessings be upon him) said: "Whoever wishes may fast on it, and whoever wishes may not fast."