Riyad as-Saliheen 1251
Ibn 'Abbas (May Allah be pleased with them) reported:
The Messenger of Allah ﷺ 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 ﷺ صام يوم عاشوراء، وأمر بصيامه. ((متفق عليه))
Classification
Sahih (Authentic)
References
Riyad as-Saliheen 1251
Riyad as-Saliheen Book of Virtues, Hadith 261