Narrated Anas ibn Malik:

When the Prophet of Allah ﷺ was lifted to the heavens (for travelling) in Paradise, or as he said, a river whose banks were of transparent or hollowed pearls was presented to him. The angel who was with him struck it with his hand and took out musk. Muhammad ﷺ then asked the angel who was with him: What is this? He replied: It is al-Kawthar which Allah has given you.

حَدَّثَنَا عَاصِمُ بْنُ النَّضْرِ، حَدَّثَنَا الْمُعْتَمِرُ، قَالَ سَمِعْتُ أَبِي قَالَ، حَدَّثَنَا قَتَادَةُ، عَنْ أَنَسِ بْنِ مَالِكٍ، قَالَ : لَمَّا عُرِجَ بِنَبِيِّ اللَّهِ ﷺ فِي الْجَنَّةِ - أَوْ كَمَا قَالَ - عُرِضَ لَهُ نَهْرٌ حَافَتَاهُ الْيَاقُوتُ الْمُجَيَّبُ أَوْ قَالَ الْمُجَوَّفُ، فَضَرَبَ الْمَلَكُ الَّذِي مَعَهُ يَدَهُ فَاسْتَخْرَجَ مِسْكًا فَقَالَ مُحَمَّدٌ ﷺ لِلْمَلَكِ الَّذِي مَعَهُ : " مَا هَذَا " . قَالَ : هَذَا الْكَوْثَرُ الَّذِي أَعْطَاكَ اللَّهُ عَزَّ وَجَلَّ .