Jami At Tirmidhi
2716
Sahih+3

Narrated Anas bin Malik:"Before he died, the Messenger of Allah (ﷺ) had written to Kisra, Ceasar, An-Najashi, and to every tyrant calling them to Allah. This An-Najashi is not the one that the Prophet (ﷺ) performed to the funeral Salat for

SahihAhmad Muhammad Shakir
SahihAl-Albani