The Prophet (peace and blessings of Allah be upon him) said: “Fasting the day of ‘Arafah I hope Allah will expiate thereby for the year before it and the year after it, and fasting the day of ‘Ashura’ I hope Allah will expiate thereby for the year that came before it.”

[Narrated by Muslim, 1162]

Abū Qatāda al-Anṣārī (raḍī Allāhu anhu) narrated that the Messenger of Allāh (ṣallallāhu ‘alayhi wa sallam) said: “…The fast of the day of `Āshūra, [I consider it to] expiate the sins of the preceding year.” [Muslim, Aḥmad, Abū Dāwūd and Ibn Khuzaymah]