Jami` at-Tirmidhi Book 47, Hadith 411
“It is a river in Paradise.” He said: “The Prophet (ﷺ) said: ‘I saw a river in Paradise, whose banks had tents were made of pearl. I said: “What is this O Jibril?’” He said: “This is Al-Kauthar which Allah has granted you.”
the Messenger of Allah said: “Indeed the first of what will be asked about on the Day of Judgment – meaning the slave (of Allah) being questioned about the favors – is that it will be said to him: ‘Did We not make your body, health, and give you of cool water to drink?’”
“While I was traveling through Paradise, a river appeared before me whose banks had tents of pearl. I said to the angel: ‘What is this?’ He said: ‘This is Al-Kauthar, which Allah has granted you.’” He said: “Then he put his hand in the clay, and removed musk from it, then I was raised up to Sidrat Al-Muntaha so I saw a magnificent light at it.”