Sahih al-Bukhari 1892
صحيح البخاري#1892SahihNarrated Ibn `Umar:The Prophet (ﷺ) observed the fast on the 10th of Muharram ('Ashura), and ordered (Muslims) to fast on that day, but when the fasting of the month of Ramadan was prescribed, the fasting of the 'Ashura' was abandoned. `Abdullah did not use to fast on that day unless it coincided with his routine fasting by chance
Scholarly Authentication
We show the most cautious grade (weakest-wins) as the overall label. Individual scholars graded it as follows:
Every narration in Sahih al-Bukhari is accepted as Sahih (authentic) by the established status of the book.
In-book reference: 30:2