The Messenger of Allah ﷺ said, "Al-Kawthar is a river in Paradise. Its banks are of gold, and it flows over pearls and rubies. Its soil is more fragrant than musk, its water sweeter than honey, and whiter than snow."He said, this is a hasan sahih hadith.
حدثنا هناد حدثنا محمد بن فضيل عن عطاء بن السائب عن محارب بن دثار
قال رسول الله ﷺ الكوثر نهر في الجنة حافتاه من ذهب ومجراه على الدر والياقوت تربته أطيب من المسك وماؤه أحلى من العسل وأبيض من الثلج قال هذا حديث حسن صحيح
Graded as hasan. Ibn Majah also narrated it in Zuhd, chapter on the description of Paradise, hadith no. 4334, from the hadith of Muhammad bin Fudayl bin Ghazwan, through the same route. Ataa's memory became mixed up, but it has many corroborating witnesses.