Hadith no. 1171 (below) is a repeat. Read it here.
Allah’s Apostle in his fatal illness said, “Allah cursed the Jews and the Christians, for they built the places of worship at the graves of their prophets.” And if that had not been the case, then the Prophet’s grave would have been made prominent before the people. So (the Prophet ) was afraid, or the people were afraid that his grave might be taken as a place for worship.
Grave of the Prophet (SAW):
Narrated Abu Bakr bin ‘Aiyash :
Sufyan At-Tammar told me that he had seen the grave of the Prophet elevated and convex.
Two types of graves: shaqq & lahd.
The shaqq means that a trench is dug in the middle of the grave to suit the size of the deceased, and its sides are built with bricks so that it will not collapse on the deceased, and the deceased is placed in it on his right side facing the qiblah, then this trench is covered with stones or the like and the ceiling is raised a little so that it will not touch the deceased, then the soil is filled in.
The lahd (niche) means that a place is dug at the bottom of the grave on the side that is closest to the qiblah, in which the deceased is placed on his right side facing the qiblah, then this hole is filled in with bricks behind the deceased, then the dirt is filled in.
Both the lahd and the shaqq are permissible according to scholarly consensus, but the lahd is preferable, because this is what was done with the grave of the Messenger (peace and blessings of Allaah be upon him). Muslim (966) narrated that Sa’d ibn Abi Waqqaas (may Allaah be pleased with him) said, during the illness of which he died: Make a lahd (niche) for me, and set up bricks over me, as was done for the Messenger of Allaah (S).
Side question: was a window opened above the Prophet (SAW)’s grave for rain? Answer here.