Musa transmitted it from Ibn Thawban, who transmitted it from ʿAṭāʾ ibn Qurrah (1), from ʿAbd-Allah ibn Ḍamrah, from Abu Hurayrah, who said:
The Messenger of Allah ﷺ said:
“Whoever would love for Allah to give him wine in the Hereafter, let him abstain from it in this world; and whoever would love for Allah to clothe him in silk in the Hereafter, let him abandon it in this world. The rivers of Paradise gush forth from beneath hills—or mountains—of musk. If the adornment of the lowest inhabitant of Paradise were placed beside the adornment of all the people of this world, what Allah—Exalted is He—will adorn him with in the Hereafter would still be superior to the adornment of all the people of this world.”

It is also narrated through the route of Abu Muʿāwiyah, from al-Aʿmash, from ʿAmr ibn Murrah, from Masrūq, from ʿAbd-Allah, who said:
“The rivers of Paradise gush forth from a mountain of musk.”
I say: this mawqūf report is the sounder one (2).

[Description of al-Kawthar, the most famous of the rivers of Paradise—may Allah grant us to drink from it by His grace and generosity]
Allah the Exalted says:
“Indeed, We have granted you al-Kawthar (1). So pray to your Lord and sacrifice (2). Indeed, your enemy is the one cut off.” [al-Kawthar: 1-3]

It is authentically established in Ṣaḥīḥ Muslim, in the narration of Muḥammad ibn Fuḍayl and ʿAlī ibn Mushir—both from al-Mukhtār ibn Fulful—from Anas, that when this surah was revealed to the Messenger of Allah ﷺ, he said:
“Do you know what al-Kawthar is?”
They replied, “Allah and His Messenger know best.”
He said, “It is a river my Lord—Exalted is He—has promised me; upon it is abundant good” (3).

In the two Ṣaḥīḥs, in the ḥadith of Shaybān, from Qatādah, from Anas, within the story of the Miʿrāj, the Prophet ﷺ said:
“I came upon a river whose banks were domes of hollow pearl. I asked, ‘What is this, O Jibrīl?’ He replied, ‘This is al-Kawthar which Allah—Exalted is He—has granted you.’”

Aḥmad likewise related it—from Ibn Abī ʿAdī, from Ḥumayd, from Anas—with this chain; and in one wording:
“I placed my hand in the channel through which its water was flowing, and it was (fragrant) pure musk” (4).

This ḥadith comes through many chains—from Anas and others among the Companions—with various wordings. Aḥmad said: “Muḥammad ibn Fuḍayl narrated to us, from al-Mukhtār ibn Fulful, from Anas, from the Prophet ﷺ, …”