To make the Heart Tender (Ar-Riqaq)

Bukhari :: Book 8 :: Volume 76 :: Hadith 566

Narrated An-Nu'man:

I heard the Prophet 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."