Messenger of Allah ﷺ forbade that the graves should be plastered or they be used as sitting places (for the people), or a building should be built over them.  

نَهَى رَسُولُ اللَّهِ ﷺ أَنْ يُجَصَّصَ الْقَبْرُ وَأَنْ يُقْعَدَ عَلَيْهِ وَأَنْ يُبْنَى عَلَيْهِ  

A hadith like this has been transmitted on the authority of Jabir b. 'Abdullah.  

سَمِعْتُ النَّبِيَّ ﷺ بِمِثْلِهِ  

Jabir said that he was forbidden to plaster graves.  

عَنْ تَقْصِيصِ الْقُبُورِ