Sayyiduna Anas bin Malik (may Allah be pleased with him) narrates: I went to the Messenger of Allah (peace and blessings be upon him), and he (peace and blessings be upon him) said: "I have been given al-Kawthar." I said: O Messenger of Allah! What is al-Kawthar? He (peace and blessings be upon him) said: "It is a river in Paradise; its width and length are equal to the distance between the east and the west. Whoever drinks from it will never be thirsty, and whoever performs ablution (wudu) from it will never be dishevelled. It will never be drunk by anyone who broke my covenant, or who killed the people of my household."
Hadith Referenceالمعجم الكبير للطبراني / باب الحاء / 2869