Musnad Ahmad 32:1540

Ibrahim ibn Abi al-Abbas narrated to us, Abu Uways narrated to us, from al-Zuhri, from his brother Abdullah ibn Muslim, that he heard Anas ibn Malik saying: A man asked the Prophet, may Allah bless him and grant him peace, about al-Kawthar, and he mentioned it, except that he said: "Its food is more delicious than it."