Anas bin Malik narrated that the Messenger of Allah (s.a.w) was asked:
"What is Al-Kawthar?" He said:"That is a river that Allah has given me"- that is, in Paradise- 'whiter than milk and sweeter than honey. In it are birds whose necks are like the necks of camels." 'Umar said: "Indeed this is plump and luxurious then." So the Messenger of Allah (s.a.w) said, "Those who consume it are more plumb than it." (ID)
English reference (ID): Vol. 4, Book 12, Hadith 2542 (ID)
Arabic reference (ID): Book 38, Hadith 2738 (ID)