Compiled by Imam Yahya ibn Sharaf al-Nawawi
عن جابر رضي الله عنه قال: نهى رسول الله صلى الله عليه وسلم أن يجصص القبر، وأن يقعد عليه، وأن يبنى عليه. ((رواه مسلم))
The Messenger of Allah (ﷺ) forbade that the graves should be plastered (made into permanent structures), used as sitting places (for the people) or building over them.[Muslim].