Sahih al-Bukhari 4964
Sahih al-Bukhari · Book 65: Prophetic Commentary on the Qur'an (Tafseer of the Prophet (pbuh)) · Chapter 1
Narrated Anas:
حَدَّثَنَا آدَمُ ، حَدَّثَنَا شَيْبَانُ ، حَدَّثَنَا قَتَادَةُ ، عَنْ أَنَسٍ ـ رضى الله عنه ـ قَالَ لَمَّا عُرِجَ بِالنَّبِيِّ صلى الله عليه وسلم إِلَى السَّمَاءِ قَالَ " أَتَيْتُ عَلَى نَهَرٍ حَافَتَاهُ قِبَابُ اللُّؤْلُؤِ مُجَوَّفًا فَقُلْتُ مَا هَذَا يَا جِبْرِيلُ قَالَ هَذَا الْكَوْثَرُ " .
When the Prophet (ﷺ) was made to ascend to the Heavens, he said (after his return), "I came upon a river the banks of which were made of tents of hollow pearls. I asked Gabriel. What is this (river?) He replied, 'This is the Kauthar.'