The Messenger of Allah ﷺ said to us, "Al-Kawthar is a river in Paradise. Its banks are of gold, and its water flows over pearls. Its water is whiter than milk and sweeter than honey."
حدثنا علي بن حفص أخبرنا ورقاء قال وقال عطاء عن محارب بن دثار
قال لنا رسول الله ﷺ الكوثر نهر في الجنة حافتاه من ذهب والماء يجري على اللؤلؤ وماؤه أشد بياضا من اللبن وأحلى من العسل
Its chain of transmission is sahih. Ali bin Hafs Madaini, his reliability was established earlier at 718, and we add here that Ibn Main, Ibn Madini, Abu Bakr bin Abu Shayba, and Abu Dawud all authenticated him. Ibn Munadi said, "Ahmad loved him intensely." Ibn Abu Hatim gave his biography in Al-Jarh wal-Tadil 3/1/182.Warqa is Ibn Umar Yashkuri, his reliability was established earlier at 692, and we add that Ibn Main and others authenticated him. Shuba said to Abu Dawud Tayalisi, "Stick with Warqa, for you will not find his like after him until he returns." Ahmad said, "Reliable, a follower of the sunnah." Bukhari gave his biography in Al-Kabir 4/2/188.Ata is Ibn Saaib.This hadith was narrated by Tirmidhi 4:219,220 through the route of Muhammad bin Fudayl from Ata bin Saaib, and he said, "A hasan sahih hadith." Ibn Kathir quoted it in his Tafsir 9:315 from this very place in the Musnad, "This is how Tirmidhi, Ibn Majah, Ibn Abu Hatim, and Ibn Jareer narrated it, through the route of Muhammad bin Fudayl from Ata bin Saaib, marfu." Tirmidhi said, "Hasan sahih."We have graded its chain sahih even though Warqa and Muhammad bin Fudayl are not mentioned among those who narrated from Ata before his memory became confused, because a longer version will come later at 9513 through the route of Hammad bin Zayd from Ata, and Hammad is among those who heard from Ata before his change. See also what has passed in the Musnad of Ibn Masud, 3787.