Shaykh Ibn Bāz (رحمه الله) was asked:1 “What is the ruling on fasting the day of Āshūrā? And is it better to fast the day before or after it? Or should we fast all of them [i.e. the day of Āshūrā and the day before and after it]? Or should we fast the day of Āshūrā alone? We hope for some clarification on that, and may Allāh reward you with goodness.”
The Shaykh (رحمه الله) responded with the following:
Fasting the day of Āshūrā is sunnah because of what has been confirmed in numerous authentic Aḥadīth from Allāh’s Messenger (ﷺ) supporting that.
It was a day the Jews used to fast because Allāh saved Mūsá and his people, and He destroyed Fir‘aun and his people.
So our Prophet, Muḥammad (ﷺ), fasted it as a form of gratitude to Allāh, and he commanded [others] to fast it.
It is [also] legislated for us to fast a day before or after it, [but] fasting the ninth [i.e. the day before] and the tenth is better. However, [whoever] fasts the tenth and the eleventh [i.e. the day after], then this will suffice in contradicting the Jews.
Whoever fasts all of them [i.e. both the day before and after Āshūrā], along with the tenth [i.e. the day of Āshūrā], then there is no problem with that because of what has come in some narrations, “Fast a day before it and a day after it.” As for fasting that day [i.e. the day of ‘Āshūrā’] alone, then it is disliked.2
Translated by: Musa Shaleem Mohammed