I heard the Prophet ﷺ forbid to sit on the grave, to plaster it with gypsum, and to build any structure over it.  

سَمِعْتُ رَسُولَ اللَّهِ ﷺ نَهَى أَنْ يُقْعَدَ عَلَى الْقَبْرِ وَأَنْ يُقَصَّصَ وَيُبْنَى عَلَيْهِ  

'Uthman said: "or anything added to it." Sulaiman b. Musa said: "or anything written on it." Musaddad did not mention in his version the words "or anything added to it." Abu Dawud said: The word "and that" (wa an) remained hidden to me.  

أَنْ يُكْتَبَ عَلَيْهِ وَلَمْ يَذْكُرْ مُسَدَّدٌ فِي حَدِيثِهِ أَوْ يُزَادَ عَلَيْهِ  

The Messenger of Allah ﷺ as saying: Allah's curse to be on the Jews, they made the graves of their Prophets mosques.  

أَنَّ رَسُولَ اللَّهِ ﷺ قَالَ قَاتَلَ اللَّهُ الْيَهُودَ اتَّخَذُوا قُبُورَ أَنْبِيَائِهِمْ مَسَاجِدَ