Sahih al-Bukhari 4965

Khalid ibn Yazid al-Kahili related to us; Israil related to us, from Abu Ishaq, from Abu Ubayda, from Aisha (may Allah be pleased with her), who said: I asked her about the words of the Exalted, ‘Indeed, We have granted you al-Kawthar.’ She said: It is a river given to your Prophet (peace and blessings be upon him), whose banks are lined with hollow pearls and whose vessels are as numerous as the stars. Zakariya, Abu al-Ahwas, and Mutarrif also transmitted it from Abu Ishaq.