*How fasting the Day of ‘Arafah is an expiation of the sins for the upcoming year.*
Al-Imām al-Mannāwi [may Allāh have mercy on him] said:
• Allāh will safeguard His slave from sinning in the coming year if he fasts on the Day of ‘Arafah.
• Allāh gives reward equal to the sins committed in the following year and this is how fasting on the Day of ‘Arafah nullifies sins.
• Allāh forgives all upcoming [minor] sins in reality and the expiator precedes the expiated.
Fayd al Qadeer, 4/230 | Al-Imām al-Mannāwi [may Allāh have mercy on him]