I heard the Messenger of Allah ﷺ forbid sitting on a grave, plastering it, or building over it.
حدثنا أحمد بن حنبل حدثنا عبد الرزاق أخبرنا ابن جريج أخبرني أبو الزبير أنه سمع
سمعت رسول الله ﷺ نهى أن يقعد على القبر وأن يقصص ويبنى عليه
Muslim narrated it in the Book of Funerals, Chapter on the prohibition of plastering graves and building over them, no. 970, from the hadith of Abdul-Razzaq through this chain, and it is in his Musannaf, no. 6488, and in Musnad Ahmad: 3/339.