Sahih Bukhari

Narrated Abu Bishr:Sa`id bin Jubair said that Ibn `Abbas said about Al-Kauthar. ""That is the good which Allah has bestowed upon His Apostle."" I said to Sa`id bin Jubair. ""But the people claim that it is a river in Paradise."" Sa`id said, ""The river in Paradise is part of the good which Allah has bestowed on His Apostle