When the verse was revealed, "Indeed, We have granted you al-Kawthar" [Kawthar 108:1], the Messenger of Allah ﷺ said, "It is a river in Paradise. Its two banks are part of Paradise, made of gold. It flows over pebbles of pearl and ruby. Its drink is sweeter than honey, whiter than milk, colder than snow, and more fragrant than the scent of musk."
لما أنزلت: {إنا أعطيناك الكوثر}، قال رسول الله ﷺ: هو نهر في الجنة، حافتاه من الجنة، حافتاه من ذهب، يجري على جنادل الدر والياقوت، شرابه أحلى من العسل، وأشد بياضا من اللبن، وأبرد من الثلج، وأطيب من ريح المسك.
Imam Ahmad (5913) and Tayalisi (2045) narrated it, and Hakim (3/543) graded it sahih, all of them through routes going back to Hammad bin Zayd, who said, Ata bin Saaib told us, he said, Muharib bin Dithar said to me, "What did you hear Saeed bin Jubayr relate from Ibn Abbas about Kawthar?" I said, "I heard him say that Ibn Abbas said, 'This is the abundant good.'" Muharib said, "Glory be to Allah! How rarely a saying is lost from Ibn Abbas. I heard Ibn Umar say," and he mentioned it, and he said, "Ibn Abbas spoke the truth. This, by Allah, is the abundant good."Its chain is sahih. Ata bin Saaib is trustworthy, and the scholars affirmed his trustworthiness, though he became confused in memory late in his life. However, Hammad bin Zayd narrated from him before that confusion set in. Hakim said, "This is a hadith sahih in chain, though the two of them (Bukhari and Muslim) did not include it."His statement, "how rarely a saying is lost," comes from the word meaning "falling away." He means that what falls away from Ibn Abbas's sayings, meaning what is inaccurate, is little. This was stated by Sindi.Then there is Ibn Abbas's saying, "Kawthar is the abundant good that Allah gave him." Bukhari (6578) narrated it from Amr bin Muhammad, who said, Hushaym told us, Abu Bishr and Ata bin Saaib informed us, from Saeed bin Jubayr, from Ibn Abbas, and he mentioned it. Abu Bishr said, "I said to Saeed, 'Some people claim that it is a river in Paradise.'" Saeed said, "The river that is in Paradise comes from the good that Allah gave him."As for what was narrated from Ibn Masud in a long hadith, "And a river will open from Kawthar to the Pool," this is daif. Imam Ahmad (3787), Bazzar in Kashf Astar (3478), and Tabarani in Al-Kabir (10/98) all narrated it through the route of Arim bin Fadl, who said, Saeed bin Zayd told us, Ali bin Hakam Banani told us, from Uthman, from Ibrahim, from Alqama and Aswad, from Ibn Masud, and he mentioned the hadith, and this is its wording.The Messenger of Allah ﷺ said, "I will indeed stand in the praised station." A man said, "O Messenger of Allah, what is that praised station?" He said, "That is when you are brought forth barefoot, naked, and uncircumcised, and the first to be clothed will be Ibrahim . Two white garments will be brought and he will be dressed in them, then he will sit facing the Throne. Then my own garment will be brought to me and I will be dressed in it, and I will stand at his right in a station that no one else will stand in, one which the earlier and later generations will envy me for. Then a river will open from Kawthar to the Pool."Its chain is daif because of Uthman, who is Ibn Umayr, diminutive form, Bajali, Abu Yaqzan, Kufi, blind. He became confused in memory, used to practice tadlis, and went to excess in his Shiism. The majority of scholars agree in declaring him daif.Bazzar said, "We do not know of it being narrated with this wording from the hadith of Alqama, from Abdullah, except through this route. Saq bin Hazn narrated from Ali bin Hakam, from Uthman bin Umayr, from Abu Waail, from Abdullah, and I suspect that Saq made an error in this chain."Through the route of Saq bin Hazn, Hakim (2/364) extracted it and said, "This is a hadith sahih in chain, though the two of them did not include it, and Uthman bin Umayr is Ibn Yaqzan." That is what he said, but the correct form is Abu Yaqzan. Dhahabi challenged him on this, saying, "No, by Allah. Daraqutni declared Uthman daif, while the rest are trustworthy."Haythami mentioned it in Al-Majmaa (10/362) and, after attributing it to Ahmad, Bazzar, and Tabarani, said, "In all of their chains is Uthman bin Umayr, who is daif."