Sahih Muslim | Book 19 | Chapter 26
Narrated by Anas
It has been narrated on the authority of Anas that the Prophet of Allah (may peace be upon him) wrote to Chosroes (King of Persia), Caesar (Emperor of Rome), Negus (King of Abyssinia) and every (other) despot inviting them to Allah, the Exalted. And this Negus was not the one for whom the Messenger of Allah (may peace be upon him) had said the funeral prayers.
Narrated by Anas b. Malik
The tradition has been narrated on the authority of Anas b. Malik (the same narrator) through a different chain of transmitters, but this version does not mention: "And he was not the Negus for whom the Prophet (may peace be upon him) had said the funeral prayers.