The Messenger of Allah ﷺ dozed for a short while and raised his smiling. He either said to them(people) or they said to him: Messenger of Allah! Why did you laugh? He said: A surah has been revealed to me just now, and then he recited: “In the name of Allah, Most Gracious. Most Merciful. To thee We have granted the fount (of abundance)” up to the end. When he recited, he asked: Do you know what al-kauthar is? They replied: Allah and his Apostle know best. He said: It is a river which my Lord, the Exalted, has promised me( to grant) in Paradise: there is abundance of good and upon it there is a pond which my people will approach on the Day of Resurrection. There are vessels as numerous as stars(in the sky). (Using translation from Abū Dāʾūd 4747)
سَمِعْتُ أَنَسَ بْنَ مَالِكٍ يَقُولُ أَغْفَى النَّبِيُّ ﷺ إِغْفَاءَةً فَرَفَعَ رَأْسَهُ مُتَبَسِّمًا إِمَّا قَالَ لَهُمْ وَإِمَّا قَالُوا لَهُ لِمَ ضَحِكْتَ؟ فَقَالَ رَسُولُ اللهِ ﷺ إِنَّهُ أُنْزِلَتْ عَلَيَّ آنِفًا سُورَةٌ فَقَرَأَ بِسْمِ اللهِ الرَّحْمَنِ الرَّحِيمِ {إِنَّا أَعْطَيْنَاكَ الْكَوْثَرَ} [الكوثر 1] حَتَّى خَتَمَهَا قَالَ هَلْتَدْرُونَ مَا الْكَوْثَرُ؟ قَالُوا اللهُ وَرَسُولُهُ أَعْلَمُ قَالَ هُوَ نَهْرٌ أَعْطَانِيهِ رَبِّي ﷻ فِي الْجَنَّةِ عَلَيْهِ خَيْرٌ كَثِيرٌ تَرِدُ عَلَيْهِ أُمَّتِي يَوْمَ الْقِيَامَةِ آنِيَتُهُ عَدَدُ الْكَوَاكِبِ يُخْتَلَجُ الْعَبْدُ مِنْهُمْ فَأَقُولُ يَا رَبِّ إِنَّهُ مِنْ أُمَّتِي فَيُقَالُ لِي إِنَّكَ لَا تَدْرِي مَا أَحْدَثُوا بَعْدَكَ