Musnad Abu Ya'la al-Mawsili 129:9

Abu Khaythama narrated to us, Yahya ibn Sa'id narrated to us, he said: Humayd narrated to us, from Anas ibn Malik, from the Prophet (peace and blessings of Allah be upon him), he said: "I entered Paradise, and suddenly I was at a river whose banks were tents of pearls. I struck my hand into the water's course, and suddenly it was pungent musk. I said: 'O Gabriel, what is this?' He said: 'This is the Kawthar which Allah has given you,' or 'which your Lord has given you.'"