(105) باب التَّشْدِيدِ فِي الْجُلُوسِ عَلَى الْقُبُورِ
It was narrated that Abu Hurairah said:
"The Messenger of Allah said: 'If any one of you were to sit on a live coal until it burns his garment, that would be better for him than sitting on a grave."
Reference: Sunan an-Nasa'i 2044
In-book reference: Book 21, Hadith 228
English translation: Vol. 3, Book 21, Hadith 2046