(33) باب النَّهْىِ عَنِ الْجُلُوسِ، عَلَى الْقَبْرِ وَالصَّلاَةِ عَلَيْهِ
Abu Huraira reported Allah's Messenger (ﷺ) as saying:
It is better that one of you should sit on live coals which would burn his clothing and come in contact with his skin than that he should sit on a grave.
Reference: Sahih Muslim 971 a
In-book reference: Book 11, Hadith 124
USC-MSA web (English) reference(deprecated numbering scheme): Book 4, Hadith 2119