Sahih al-Bukhari 2840
صحيح البخاري#2840SahihNarrated Abu Sa`id:I heard the Prophet (ﷺ) saying, "Indeed, anyone who fasts for one day for Allah's Pleasure, Allah will keep his face away from the (Hell) fire for (a distance covered by a journey of) seventy years
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: 56:56