Ibne Abbas said: When Surah Kawthar was revealed to the Prophet (s.a.w.a.), Ali b. Abi Talib (a.s.) asked him – What is Kawthar, O Messenger of Allah?
The Prophet (s.a.w.a.) replied – It is a river with which Allah has honoured me.
Ali (a.s) said – This is an honourable river. O Prophet! Describe it for me.
The Prophet (s.a.w.a.) replied – O Ali! It starts from under the Throne of Allah. The water is whiter than milk, sweeter than honey, and softer than butter. The stones there are aquamarines, sapphire, and coral. The grass by the river is saffron and the sand is musk. The base of this river is under the Throne of Allah.”
Then the Prophet (s.a.w.a.) put his arm around Ali (a.s.) and informed – O Ali, this river is for me, for you, and for those who love you after me.
Al-Amaali v 1 p 67 Al-Amaali P 294 Behaar al-Anwaar v 8 p 17