Sahih Bukhari
To make the Heart Tender (Ar-Riqaq)
Volume: 008 / Book Number: 076 / Hadith Number: 580
Narrated Ibn 'Abbas:
The word 'Al-Kauthar' means the abundant good which Allah gave to him (the Prophet Muhammad). Abu Bishr said: I said to Said, "Some people claim that it (Al-Kauthar) is a river in Paradise." Said replied, "The river which is in Paradise is one item of that good which Allah has bestowed upon him (Muhammad)."