Musannaf Ibn Abi Shaybah

Ibrahim narrates that a lahd (niche) was made for the Messenger of Allah, peace and blessings be upon him, and his blessed grave was raised so much that it could be recognized.

Hazrat Abdullah bin Abi Bakr says that I saw the grave of Hazrat Usman bin Maz'oon, which was elevated (raised above the ground).

Hazrat Ata bin Abi Maimunah narrates from his father that Hazrat Imran bin Husain had instructed in his will that his grave should be made square. It should be raised (high) enough that it is four fingers above the ground.