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.  

قَالَ رَسُولُ اللَّهِ ﷺ لأَنْ يَجْلِسَ أَحَدُكُمْ عَلَى جَمْرَةٍ فَتُحْرِقَ ثِيَابَهُ فَتَخْلُصَ إِلَى جِلْدِهِ خَيْرٌ لَهُ مِنْ أَنْ يَجْلِسَ عَلَى قَبْرٍ