Fast of 10th Muharram Atones a Year’s Sins

Abu Qatada (radi Allahu anhu) relates that the Prophet (sal Allahu alaihi wa sallam) said that the fast on the 10th of Muharram atones for the sins of the preceding year. [Sahih Muslim]

It is reported from Abu Hurairah (radi Allahu anhu) that the Prophet (sal Allahu alaihi wa sallam) said that after Ramadan, the fasts of Muharram have the greatest excellence. [Sahih Muslim]

The 10th of Muharram was the day that Allah (subhana wa ta’ala) delivered Musa (alaihis salam) and the Bani Israil from Egypt and drowned Firaun and his people. Musa (alaihis salam) thus observed fast on this day out of gratitude to Allah (subhana wa ta’ala).

When the Prophet (sal Allahu alaihi wa sallam) came to Madina he found the Jews fasting on this day for this reason. Because Muslims follow unaltered revelation, they are closer to Musa (alaihis salam) than the Jews are. Thus, Allah (subhana wa ta’ala) inspired Rasul Allah (sal Allahu alaihi wa sallam) to fast on the tenth of Muharram too and tell the Muslims to fast on that day as well. But to distinguish ourselves from the Jews, Rasul Allah (sal Allahu alaihi wa sallam) told us to fast on either the 9th or the 11th along with the 10th. [Sahih Bukhari]