Why does ‘Āshurā expiate [the sins] of a year and the Day of ‘Arafah expiates that of two years?’
Al-Imām ibn al-Qayyim [may Allāh have mercy on him] said: “There is two viewpoints:
‘The first: The Day of ‘Arafah is in a sacred month, [the month] before it is a sacred month; and [the month] after it is a sacred month, in contrast to ‘Āshurā.
The second: fasting the Day of ‘Arafah is from the exclusive characteristics of our legislation, in contrast to ‘Ashurā.”
Badā’i’ al-Fawāid, 4/211 | Al-Imām ibn al-Qayyim [may Allāh have mercy on him]