Sahih Bukhari Volume 8, Book 81, Hadith 6580

حَدَّثَنِي عَمْرُو بْنُ مُحَمَّدٍ، حَدَّثَنَا هُشَيْمٌ، أَخْبَرَنَا أَبُو بِشْرٍ، وَعَطَاءُ بْنُ السَّائِبِ، عَنْ سَعِيدِ بْنِ جُبَيْرٍ، عَنِ ابْنِ عَبَّاسٍ ـ رضى الله عنه ـ قَالَ الْكَوْثَرُ الْخَيْرُ الْكَثِيرُ الَّذِي أَعْطَاهُ اللَّهُ إِيَّاهُ‏.‏ قَالَ أَبُو بِشْرٍ قُلْتُ لِسَعِيدٍ إِنَّ أُنَاسًا يَزْعُمُونَ أَنَّهُ نَهَرٌ فِي الْجَنَّةِ‏.‏ فَقَالَ سَعِيدٌ النَّهَرُ الَّذِي فِي الْجَنَّةِ مِنَ الْخَيْرِ الَّذِي أَعْطَاهُ اللَّهُ إِيَّاهُ‏.‏

Narrated By 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)."