Sahih Muslim
The Book of Prayers (Kitab Al-Salat)
Book Number: 004 / Hadith Number: 2114
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 (may peace be upon him) commanding (us) to level the grave.