He said: Abul Hasan ALI b. Bilal al-Mahlabi, reported to me from Abu al-Abbas Ahmad b. al-Hasan al-Baghdadi, who reported from Muhammad b. Ismail, who reported from Muhammad b. al-Swalt, who reported from Abu Kudainah, from Ata, from Saeed b. Jubair, from Abdullah Ibn al-Abbas, who said:
When the verse: 'We have surely blessed you with abundance' (Kauthar-108:1) was revealed to the PROPHET (SAWW) , peace be upon him and his progeny, ALI BIN ABI TALIB (ASWS), peace be upon him, asked him: "O MESSENGER of ALLAH (SWT), what is al-Kauthar?" He said: "It is a stream with which ALLAH (SWT) has honoured me." Then ALI (ASWS) , peace be upon him, said: "O MESSENGER of ALLAH (SWT), describe for us this sacred stream." He said: "Yes, O ALI (ASWS) , al- Kauthar is a stream that flows under the Throne of ALLAH (SWT), Most High. Its water is whiter than milk, sweeter than honey, softer than cream. Its pebbles are of aquamarine, ruby and coral. Its weeds are saffron, its dust is sweet smelling musk, and its basins are under the Throne of ALLAH (SWT), Most High!" Then the Prophet, peace be upon him and his progeny, struck his hand on AMIRUL MO’MINEEN (ASWS)'s side and said: "O ALI (ASWS) , this stream is for me and you, and for those who love you after I have gone."
(Ref Al Amali Shaikh Mufeed The Thirty Fifth assembly Hadees No.5)