From Sahih Muslim (Hadith 2242):
Thumama b. Shafayy reported:When we were with Fadala b. 'Ubaid in the country of the Romans at a place (known as) Rudis, a friend of ours died. Fadala b. 'Ubaid ordered to prepare a grave for him and then it was levelled; and then he said: I heard the Messenger of Allah (ﷺ) commanding (us) to level the grave
Reference: Muslim 2242