Sayyiduna Abu Hurayrah (may Allah be pleased with him) said that the Messenger of Allah (peace and blessings be upon him) said: "If a person sits on a live coal, or on fire, and it burns through his clothes until it reaches him, that is better for him than that he sits on a grave."
In the narration of Ali (bin Asim) it is: "That one of you sits on a live coal and it burns his clothes until it reaches his skin is better for him than that he sits on a grave."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الجنائز / 7214