https://www.wrightstreetmosque.com/why-does-fasting-on-the-day-of-arafah-expiate-the-sins-of-2-years-whilst-ashuraa-expiates-that-of-1-year/
Why Does Fasting on the Day of ‘Arafah Expiate the Sins of 2 years Whilst ‘Ashuraa Expiates That of 1 Year?