The Messenger of Allah ﷺ was asked, "What is al-Kawthar?"He replied, "It is a river Allah has given me in Paradise, whiter than milk and sweeter than honey. In it are birds whose necks are like the necks of camels."Umar remarked, "These birds are indeed luxurious."The Messenger of Allah ﷺ said, "Those who eat them are even better off."
حدثنا عبد بن حميد أخبرنا عبد الله بن مسلمة عن محمد بن عبد الله بن مسلم عن أبيه
سئل رسول الله ﷺ ما الكوثر قال ذاك نهر أعطانيه الله يعني في الجنة أشد بياضا من اللبن وأحلى من العسل فيها طير أعناقها كأعناق الجزر قال عمر إن هذه لناعمة قال رسول الله ﷺ أكلتها أحسن منها
[Its isnad is sahih] Ahmad (3/236) also narrated it from the hadith of Muhammad bin Abdullah, the nephew of Zuhri, and Nasai in Al-Kubra (no. 11703) from the hadith of Abdullah bin Muslim bin Shihab through the same route. Zuhri narrated it (Hakim 2/537), and Abdul-Wahhab bin Abu Bakr (Ahmad 3/236, 237) narrated it from Abdullah bin Muslim through the same route.