Abdullah bin Umar reported,

When the verse was revealed, "Indeed, We have granted you al-Kawthar" [Kawthar 108:1], the Messenger of Allah ﷺ said, "It is a river in Paradise. Its two banks are part of Paradise, made of gold. It flows over pebbles of pearl and ruby. Its drink is sweeter than honey, whiter than milk, colder than snow, and more fragrant than the scent of musk."

Azami 811

Sahih

عن ابن عمر، قال

لما أنزلت: {إنا أعطيناك الكوثر}، قال رسول الله ﷺ: هو نهر في الجنة، حافتاه من الجنة، حافتاه من ذهب، يجري على جنادل الدر والياقوت، شرابه أحلى من العسل، وأشد بياضا من اللبن، وأبرد من الثلج، وأطيب من ريح المسك.

الأعظمي 811صحيح
Contents
Reference
Commentary
Ayat
Collection
Jami al-Kamil
Book
Faith
Chapter
Faith in the Prophet ﷺ
Section
Kawthar which Allah gave to His Prophet ﷺ and its attributes
Numbering
Jami al-Kamil 811 (2nd edition)
Azami 811