Abu Qatada (Allah be pleased with him) related that the Messenger of Allah (blessings and peace be upon him, his family, and companions) said, “Fasting the Day of `Arafah [9th of Dhu’l Hijjah] expiates for two years, one prior and one forthcoming. And fasting the Day of ` Ashura [10th of Muharram] expiates for the past year.”[Reported by Muslim, Abu Dawud, Nasa’i, and Ibn Majah]