Sahih Muslim
The Book of Prayers (Kitab Al-Salat)
Book Number: 004 / Hadith Number: 791
Mukhtar b. Fulful reported that he had heard Anas b. Malik say that the Messenger of Allah (may peace be upon him) 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.