The Messenger of Allah ﷺ used to fast on Ashura and commanded others to fast it.
حدثنا أبو بكر بن أبي شيبة حدثنا يزيد بن هارون عن ابن أبي ذئب عن الزهري عن عروة
كان رسول الله ﷺ يصوم عاشوراء ويأمر بصيامه
No references are available.
Bukhari narrated it in the Book of Fasting, Chapter on Fasting the Day of Ashura, no. 2001, and Muslim in the Book of Fasting, Chapter on Fasting the Day of Ashura, no. 1125, and others besides them, from Zuhri with this chain, at greater length, and it includes, "Then when Ramadan was made obligatory, whoever wished fasted the Day of Ashura, and whoever wished broke his fast."