Anas reported from the Prophet ﷺ that he said, "While I was walking in Paradise, I came upon a river whose banks were domes of hollowed pearls.I asked, 'Jibreel, what is this?'He replied, 'This is al-Kawthar, which your Lord has given you.' And there I found its clay," or he said, "its fragrance, was strong-scented musk."
عن النبي ﷺ قال: بينما أنا أسير في الجنة، إذا أنا بنهر حافتاه قباب الدر المجوف. قلت: ما هذا يا جبريل؟ قال: هذا الكوثر الذي أعطاك ربك، فإذا طينه أو طيبه مسك أذفر.
Bukhari narrated it in the Chapter on Heart-Softening Matters (6581) from Abu Walid and Hudba bin Khalid, both of them from Hammam, who said, Qatada narrated to us, who said, Anas bin Malik narrated to us, and he mentioned it.