Sahih al-Bukhari 1898
صحيح البخاري#1898SahihNarrated Abu Huraira:Allah's Messenger (ﷺ) said, "When Ramadan begins, the gates of Paradise are opened
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: 30:8