عن أبي قتادة أن رجلا سأل النبي صلى الله عليه وسلم فقال: يا رسول الله أرأيت رجلا يصوم يوم عاشوراء قال: ذاك صوم سنة قال: أرأيت رجلا يصوم يوم عرفة قال: يكفر السنة وما قبلها (صحيح ابن حبان، الرقم:3631)

Hazrat Abu Qataadah (radhiyallahu ‘anhu) reports that a Sahaabi once asked Rasulullah (sallallahu ‘alaihi wasallam), “O Rasulullah (sallallahu ‘alaihi wasallam), what is the reward of the person who fasts on the day of Aashuraa?” Nabi (sallallahu ‘alaihi wasallam) replied, “It carries the reward of fasting for an entire year.”

The Sahaabi then asked, “What is the reward of fasting on the day of Arafah?” Rasulullah (sallallahu ‘alaihi wasallam) replied, “It expiates the (minor) sins of the present year and the previous year.”