"Indeed the person among the inhabitants of the Fire punished least [on the Day of Judgment] is a man who has two coals beneath his feet, which cause his brain to boil." Other chains report similar narrations.  

أَنَّ رَسُولَ اللَّهِ ﷺ قَالَ إِنَّ أَهْوَنَ أَهْلِ النَّارِ عَذَابًا يَوْمَ الْقِيَامَةِ رَجُلٌ فِي إِخْمَصِ قَدَمَيْهِ جَمْرَتَانِ يَغْلِي مِنْهُمَا دِمَاغُهُ