Musnad Ahmad 27:2016

He said: I found this hadith in my father’s book in his own handwriting: Ali ibn Hafs narrated to us, Waraqa narrated to us, from ‘Ata’—meaning Ibn al-Sa’ib—from Ibn Jubayr: "{Indeed, We have granted you al-Kawthar} [Al-Kawthar: 1] is the abundant good." And ‘Ata’ said, from Muharib ibn Dithar, from Ibn ‘Umar, he said: The Messenger of Allah, may Allah bless him and grant him peace, said to us: "Al-Kawthar is a river in Paradise, its banks are of gold, and the water runs over pearls, and its water is whiter than milk and sweeter than honey."