The existence of the Spring of Kausar is found in the Qur’an and the traditions, it is the abundance (Khayre Kaseer) which was bestowed on the Prophet (s).

On the Day of Judgment, every Prophet will have a Houz (tank) and the Houz of our Holy Prophet (Sallallahu alaihi wa sallam) is called Houz-e-Kauthar. Its length will be equal to a day’s march. Its soil will be musk, very fragrant. Its water will be whiter than milk and sweeter than honey, more fragrant than musk and cooler than ice. The vessels in which it is drunk will be shining like stars. The Holy Prophet (Sallallahu alaihi wa sallam) will give it to His followers with His own blessed hands. Whoever drinks once will not feel thirsty again.

There is a Hadith in Sahih Bukhari:

Translation of Hadith: It has been narrated on the authority of Hadhrat Anas (May Allah be well pleased with him), he said: The Holy Prophet (Sallallahu alaihi wa sallam) said: When I was walking in Jannah, I suddenly came upon a stream, on both sides of which are tents of pearls, which are carved from the inside. I said: O Jibrail (Peace be upon him)! What is this? He said: This is the Kauthar which your Lord has granted you. I saw that its soil is fragrant musk.

(Sahih Bukhari, Hadith No: 6581)