Riyad as-Salihin, Book 9, Hadith 1251 (In-Book) ⓘ
Ibn 'Abbas (May Allah be pleased with them) reported: The Messenger of Allah observed Saum (fasting) on the day of 'Ashura' and commanded us to fast on this day.[Al-Bukhari and Muslim].
وعن ابن عباس رضي الله عنهما أن رسول الله صلى الله عليه وسلم صام يوم عاشوراء، وأمر بصيامه. ((متفق عليه))