The Messenger of Allah ﷺ as saying: It is better that one of you should sit on the live coals which burns his clothing and come in contact with his skin than that he should sit on a grave. (Using translation from Abū Dāʾūd 3228)
عَنِ النَّبِيِّ ﷺ قَالَ لَأَنْ يَجْلِسَ أَحَدُكُمْ عَلَى جَمْرَةٍ فَتُحْرِقَ ثِيَابَهُ حَتَّى تَخْلُصَ إِلَيْهِ خَيْرٌ لُهُ مِنْ أَنْ يَطَأَ عَلَى قَبْرِ رَجُلٍ مُسْلِمٍ