"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. (Using translation from Tirmidhī 2604)
سَمِعْتُ رَسُولَ اللهِ ﷺ يَقُولُ إِنَّ أَهْوَنَ أَهْلِ النَّارِ عَذَابًا يَوْمَ الْقِيَامَةِ رَجُلٌ يُجْعَلُ فِي أَخْمَصِ قَدَمَيْهِ نَعْلَانِ مِنْ نَارٍ يَغْلِي مِنْهُمَا دِمَاغُهُ