ENOfficial
Narrated An-Nu`man: 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."
Source: sunnah.com
Other translations
Arabic
حَدَّثَنِي مُحَمَّدُ بْنُ بَشَّارٍ، حَدَّثَنَا غُنْدَرٌ، حَدَّثَنَا شُعْبَةُ، قَالَ سَمِعْتُ أَبَا إِسْحَاقَ، قَالَ سَمِعْتُ النُّعْمَانَ، سَمِعْتُ النَّبِيَّ صلى الله عليه وسلم يَقُولُ "إِنَّ أَهْوَنَ أَهْلِ النَّارِ عَذَابًا يَوْمَ الْقِيَامَةِ لَرَجُلٌ تُوضَعُ فِي أَخْمَصِ قَدَمَيْهِ جَمْرَةٌ يَغْلِي مِنْهَا دِمَاغُهُ".
sunnah.com