Sahih al-Bukhari 2002
صحيح البخاري#2002SahihNarrated Aisha:Quraish used to fast on the day of 'Ashura' in the Pre-Islamic period, and Allah's Messenger (ﷺ) too, used to fast on that day. When he came to Medina, he fasted on that day and ordered others to fast, too. Later when the fasting of the month of Ramadan was prescribed, he gave up fasting on the day of 'Ashura' and it became optional for one to fast on it or not
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: 30:107