Sahih al-Bukhari 6578
صحيح البخاري#6578SahihNarrated Ibn `Abbas:The word 'Al-Kauthar' means the abundant good which Allah gave to him (the Prophet Muhammad (ﷺ)). Abu Bishr said: I said to Sa`id, "Some people claim that it (Al-Kauthar) is a river in Paradise." Sa`id replied, "The river which is in Paradise is one item of that good which Allah has bestowed upon him (Muhammad)
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: 81:166