To make the Heart Tender (Ar-Riqaq)
Ṣaḥīḥ al-Bukhārī 6561
إِنَّ أَهْوَنَ أَهْلِ النَّارِ عَذَابًا يَوْمَ الْقِيَامَةِ لَرَجُلٌ تُوضَعُ فِي أَخْمَصِ قَدَمَيْهِ جَمْرَةٌ يَغْلِي مِنْهَا دِمَاغُهُ
inna ahwana ahli an-nāri ʿadhāban yawma al-qiyāmah larajulun tūḍaʿu fī akhmaṣi qadamayhi jamratun yaghlī minhā dimāghuhu
Transliteration generated from the Arabic vowel marks
The full narration
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
Ṣaḥīḥ al-Bukhārī · 6561
Ṣaḥīḥ