Riyad as-Salihin, Book 9, Hadith 1250 (In-Book) ⓘ
Abu Qatadah (May Allah be pleased with him) reported: The Messenger of Allah was asked about the observance of Saum (fasting) on the day of 'Arafah. He said, "It is an expiation for the sins of the preceding year and the current year."[Muslim].
وعن أبي قتادة رضي الله عنه قال: سئل رسول الله صلى الله عليه وسلم: عن صوم يوم عرفة؟ قال: "يكفر السنة الماضية والباقية" ((رواه مسلم)).