Sahih muslim:400b Chapter: The Beginning Of The Adhan Book 4, Hadith 57

Mukhtar b. Fulful reported that he had heard Anas b. Malik say that the Messenger of Allah (ﷺ) dozed off, and the rest of the hadith is the same as transmitted by Mus-hir except for the words that he (the Holy Prophet) said: It (Kauthar) is a canal which my Lord the Exalted and the Glorious has promised me in Paradise. There is a tank over it, but he made no mention of the tumblers like the number of the stars.