07/08/2022
Abu Qatadah reported: The Prophet, peace and blessings be upon him, was asked about fasting the day of Arafat and he said, “It will expiate the sins of the previous and upcoming years.” Then, the Prophet was asked about fasting the day of Ashura and he said, “It will expiate the sins of the past year.”
Source: Ṣaḥīḥ Muslim 1162