I heard the Prophet ﷺ say, "The person of the Fire who will receive the lightest punishment on the Day of Resurrection is a man under the arch of whose feet a burning ember will be placed, causing his brain to boil from it."
سمعت النبي ﷺ يقول: إن أهون أهل النار عذابا يوم القيامة لرجل توضع في أخمص قدميه جمرة يغلي منها دماغه.
Bukhari related it in the Book of Raqaiq (6561), and Muslim in the Book of Iman (213), both from Muhammad bin Bashshar, who said, Ghundar narrated to us, who said, Shubah narrated to us, who said, I heard Abu Ishaq say, I heard Numan bin Bashir, and he then related the hadith. The wording given here is Bukhari's.Muslim also related it from Muhammad bin Muthanna, from Ghundar, and in his version it reads, "Two embers are placed in the hollow of his feet, causing his brain to boil." It also appears in Bukhari (6562) through the route of Israil, from Abu Ishaq, with an addition at the end, "just as a cauldron or a copper vessel boils."Muslim also related it through another route, from Amash, from Abu Ishaq, "The person with the lightest punishment among the people of Hell will be one who has two sandals and two straps of fire, causing his brain to boil just as a cauldron boils. He will not think that anyone is being punished more severely than he is, yet his is the lightest punishment of all."As for the word "akhmas," it refers to the part of the foot that is raised off the ground and does not touch it. As for "shirakan," the shirak is one of the straps of a sandal, the one that lies across the top of the sandal and over the top of the foot. As for "mirjal," it refers to a cooking vessel, whether made of iron, copper, stone, or pottery.