Imam Al-Nawawi’s Riyad-us-Saliheen
Chapter 347
Prohibition of Sitting on the Graves
1766. Abu Hurairah (May Allah be pleased with him) said: The Messenger of Allah (sallallaahu alayhi wa sallam) said, “It is much better for one of you to sit on a live coal, which will burn his clothes and get to his skin than to sit on a grave.”
[Muslim].
AbdurRahman.Org 