Language:
كتاب الرقاق
81  
To make the Heart Tender (Ar-Riqaq)
(51)
Chapter: The description of Paradise and the Fire
(51)
باب صِفَةِ الْجَنَّةِ وَالنَّارِ
Sahih al-Bukhari 6561

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."

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"‏.‏
Reference : Sahih al-Bukhari 6561
In-book reference : Book 81, Hadith 150
USC-MSA web (English) reference : Vol. 8, Book 76, Hadith 566
  (deprecated numbering scheme)
Sahih al-Bukhari 6562

Narrated An-Nu`man bin Bashir:

I heard the Prophet (ﷺ) saying, "The least punished person of the (Hell) Fire people on the Day of Resurrection will be a man under whose arch of the feet two smoldering embers will be placed, because of which his brain will boil just like Al-Mirjal (copper vessel) or a Qum-qum (narrow-necked vessel) is boiling with water."

حَدَّثَنَا عَبْدُ اللَّهِ بْنُ رَجَاءٍ، حَدَّثَنَا إِسْرَائِيلُ، عَنْ أَبِي إِسْحَاقَ، عَنِ النُّعْمَانِ بْنِ بَشِيرٍ، قَالَ سَمِعْتُ النَّبِيَّ صلى الله عليه وسلم يَقُولُ ‏ "‏ إِنَّ أَهْوَنَ أَهْلِ النَّارِ عَذَابًا يَوْمَ الْقِيَامَةِ رَجُلٌ عَلَى أَخْمَصِ قَدَمَيْهِ جَمْرَتَانِ يَغْلِي مِنْهُمَا دِمَاغُهُ، كَمَا يَغْلِي الْمِرْجَلُ وَالْقُمْقُمُ‏"‏‏.‏
Reference : Sahih al-Bukhari 6562
In-book reference : Book 81, Hadith 151
USC-MSA web (English) reference : Vol. 8, Book 76, Hadith 567
  (deprecated numbering scheme)