عَنْ أَبِي قَتَادَةَ رَضِيَ اللَّهُ عَنْهُ قَالَ: قَالَ رَسُولَ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَآلِهِ وَسَلَّمَ: ((صَوْمُ يَوْمِ عَرَفَةَ يُكَفِّرُ سَنَتَيْنِ مَاضِيَةً وَمُسْتَقْبَلَةً، وَصَوْمُ عَاشُورَاءَ يُكَفِّرُ سَنَةً مَاضِيَةً))
It is narrated from Sayyiduna Abu Qatadah (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said: Fasting on the Day of Arafah, that is, the 9th of Dhul-Hijjah, becomes an expiation for the sins of the previous and the coming two years, and fasting on the Day of Ashura is an expiation for the sins of the previous year.