عَنْ أَبِي هُرَيْرَةَ رَضِيَ اللَّهُ عَنْهُ يَرْفَعُهُ إِلَى النَّبِيِّ صَلَّى اللَّهُ عَلَيْهِ وَآلِهِ وَسَلَّمَ قَالَ: ((لَأَنْ يَجْلِسَ أَحَدُكُمْ عَلَى جَمْرَةٍ فَتُحْرِقَ ثِيَابَهُ حَتَّى تُفْضِيَ إِلَى جِلْدِهِ خَيْرٌ لَهُ مِنْ أَنْ يَجْلِسَ عَلَى قَبْرٍ (وَفِي لَفْظٍ) خَيْرٌ مِنْ أَنْ يَطَأَ عَلَى قَبْرِ رَجُلٍ مُسْلِمٍ))
It is narrated from Sayyiduna Abu Hurairah, may Allah be pleased with him, that the Noble Prophet, peace and blessings be upon him, said: If any one of you were to sit on burning coals that burn his clothes and reach his skin, that would be better for him than sitting on a grave. In another narration: That would be better for him than trampling on a Muslim's grave.