Sahih al-Bukhari 2006
صحيح البخاري#2006SahihNarrated Ibn `Abbas:I never saw the Prophet (ﷺ) seeking to fast on a day that he favored more than another except this day, the day of 'Ashura', and this month, meaning the month of Ramadan
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: 30:111