Sahih al-Bukhari 2000
صحيح البخاري#2000SahihNarrated Salim's father:The Prophet (ﷺ) said, "Whoever wishes may fast on the day of 'Ashura
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: 30:105