The Prophet ﷺ said, "Fasting on the Day of Ashura, I expect from Allah that it will expiate the sins of the year before it."
حدثنا قتيبة وأحمد بن عبدة الضبي قالا حدثنا حماد بن زيد عن غيلان بن جرير عن عبد الله بن معبد
أن النبي ﷺ قال صيام يوم عاشوراء إني أحتسب على الله أن يكفر السنة التي قبله
[Sahih] Previously mentioned: 749. There are also reports on this topic from Ali, [Abdullah bin Ahmad in the supplements to the Musnad: 1/129], Muhammad bin Sayfi [Ibn Majah, no. 1735], Salama bin Akwa [Bukhari, no. 1924, and Muslim, no. 1135], Hind bin Asma [Ahmad: 3/484], Ibn Abbas [coming up: 754, 755], Rabee bint Muawwidh bin Afra [Bukhari, no. 1960, and Muslim, no. 1136], Abdul-Rahman bin Salama Khuzai from his uncle [Tahawi in Maani al-Athar: 2/73], and Abdullah bin Zubayr [Ahmad: 4/5, 6].