Jami` at-Tirmidhi Book 47, Hadith 410
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?’”
“When this Ayah was revealed: ‘Then on that Day, you shall be asked about the delights!’ the people said: ‘O Messenger of Allah! About which delights shall we be asked? For they are only the two black things, while the enemy is present and our swords are (at the ready) upon our shoulders?” He said: ‘But it is what shall come.’”
“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.”