Sunan an Nasai
2030
Sahih+2

Thumamah bin Shufa narrated:"We were with Fadalah bin 'Ubaid in the land of the Romans, and a companion of ours died. Fadalah ordered that his grave be made level, then he said: 'I heard the Messenger of Allah commanding that it be made level

SahihAbu Ghuddah
SahihAl-Albani