I heard the Prophet ﷺ saying, "The person who will have the least punishment from amongst the Hell Fire people on the Day of Resurrection, will be a man under whose arch of the feet a smoldering ember will be placed so that his brain will boil because of it." (Using translation from Bukhārī 6561)
سَمِعْتُ رَسُولَ اللهِ ﷺ يَقُولُ إِنَّ أَهْوَنَ أَهْلِ النَّارِ عَذَابًا يَوْمَ الْقِيَامَةِ لَرَجُلٌ يُوضَعُ فِي أَخْمَصِ قَدَمَيْهِ جَمْرَتَانِ يَغْلِي مِنْهُمَا دِمَاغُهُ