Bismillahir Rahmanir Rahim.

RasoolAllah Sallallahu alayhi wa ala Alihi wa sallam se Ashura (10 Muharram) ke din ke Rozey ke bare mein pucha to Aap Sallalahu alayhi wa ala Alihi wa sallam ne faramaya yeh Guzrey huye Saal ke Gunahon ka Kaffara hai.

Hadith English:
Messenger of Allah (peace and blessings of Allaah be upon him and his family) was asked about fasting on the day of ‘Ashura (10th of Muharram), whereupon he said: It expiates the sins of the preceding year.

[Sahih Muslim, Book 006, Number 2603]