Observing Sawm on the ninth and tenth of Muharram is better than on the tenth and eleventh
What is the ruling on observing Sawm (Fast) on the Day of ‘Ashura’ (10th of Muharram)? Is it better to observe Sawm on the day that precedes it, the day that succeeds it, all the three days, or on the Day of ‘Ashura’ only? Please clarify the matter. May Allah reward you with the best!
It is a Sunnah (supererogatory act of worship following the example of the Prophet) to observe Sawm on the Day of ‘Ashura’ for the authentic Hadiths in which the Prophet (peace be upon him) stated so. The Prophet (peace be upon him) mentioned that the Jews used to observe Sawm on that Day because it was the day on which Allah (may He be Exalted) rescued Prophet Musa (Moses, peace be upon him) and his people and destroyed Pharaoh and his people. Our Prophet Muhammad thus, observed Sawm on the Day of ‘Ashura’ to express his gratitude to Allah, advised Muslims to do so, and directed us as well to observe Sawm on the day preceding or succeeding it. However, observing Sawm on the ninth and tenth of Muharram is better than doing so on the tenth and eleventh. The latter form is also sufficient for it contradicts the practice of the Jews as well. One may also observe Sawm on all three days, i.e. the ninth, the tenth, and the eleventh of Muharram as is reported in some narrations: Fast a day before (the Day of ‘Ashura’) and a day after it. But, it is Makruh (reprehensible) to observe Sawm on the Day of ‘Ashura’ only, i.e. without accompanying it by the preceding or the succeeding day. May Allah grant us success!
Source: Fatwas of Ibn Baz