Sahih Muslim — The Book of Prayers — Hadith No: 894
Translation
Anas reported:One day the Messenger of Allah (ﷺ) was sitting amongst us that he dozed off. He then raised his head smilingly. We said: What makes you smile. Messenger of Allah? He said: A Sura has just been revealed to me, and then recited: In the name of Allah, the Compassionate, the Merciful. Verily We have given thee Kauthar (fount of abundance). Therefore turn to thy Lord for prayer and offer sacrifice, and surely thy enemy is cut off (from the good). Then he (the Holy Prophet) said: Do you know what Kauthar is? We said: Allah and His Messenger know best. The Prophet (ﷺ) said: It (Kauthar) is a canal which my Lord, the Exalted and Glorious has promised me, and there is an abundance of good in it. It is a cistern and my people would come to it on the Day of Resurrection, and tumblers there would be equal to the number of stars. A servant would be turned away from (among the people gathered there). Upon this I would say: My Lord, he is one of my people, and He (the Lord) would say: You do not know that he innovated new things (in Islam) after you. Ibn Hujr made this addition in the hadith:" He (the Holy Prophet) was sitting amongst us in the mosque, and He (Allah) said: (You don't know) what he innovated after you