It is narrated from Hazrat Anas (may Allah be pleased with him) that the Messenger (peace and blessings be upon him) said: I entered Paradise and suddenly saw a river, on both banks of which were tents made of pearls. I put my hand in and caught something flowing in the water, and it was fragrant musk. I asked Jibreel, "What is this?" He replied, "This is the River Kawthar which Allah has granted to you."
Hadith Referenceمسند احمد / مسند المكثرين من الصحابة / 14079