Sahih Bukhari Volume 8, Book 76, Hadith Number 567.

Narated By An-Nu’man bin Bashir : I heard the Prophet 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.”