On the night the Messenger of Allah ﷺ was taken on the Night Journey from the Sacred Mosque of the Kaabah. He then recounted the lengthy hadith of the Night Journey and the Ascension, in which it was mentioned,When he was in the lowest heaven, he saw two rivers flowing.He asked, "What are these two rivers, Jibreel?"Jibreel replied, "These are the Nile and the Furat at their source."Then Jibreel took him further through the heaven, and there he came upon another river, beside which stood a palace of pearl and emerald. He struck his hand into it, and found it to be musk of the finest fragrance.He asked, "What is this, Jibreel?"Jibreel answered, "This is al-Kawthar, which your Lord has reserved for you."
ليلة أسري برسول الله ﷺ من مسجد الكعبة. فذكر حديث الإسراء والمعراج بطوله وجاء فيه: فإذا هو في السماء الدنيا بنهرين يطردان، فقال ما هذان النهران يا جبريل، قال: هذا النيل والفرات عنصرهما، ثم مضى به في السماء، فإذا هو بنهر آخر عليه قصر من لؤلؤ وزبرجد فضرب يده، فإذا هو مسك أذفر. قال: ما هذا يا جبريل قال: هذا الكوثر الذي خبأ لك ربك.
Bukhari related it in the Book of Tawheed (7517), and Muslim in the Book of Iman (162), both from the hadith of Sulayman bin Bilal, from Sharik bin Abdullah, who said, "I heard Ibn Malik saying," and then he mentioned the hadith at length. Refer to it in full in the chapter on Isra and Miraj. His statement, "their origin," means their source.