"We are told of a saying of the Holy Prophet(saw) in a Hadith: 'The lightest punishment a man will receive on the Day of Resurrection will be that two sparks will be placed below his soles. But they will be so severe that because of them the man's brain will boil and he will suppose that he is being given the severest of punishments.' Some narrations state that this punishment will be awarded to the paternal uncle of the Holy Prophet(saw), Abu Talib because he had been very helpful to the Holy Prophet(saw) but did not profess faith until his last breath. Allah knows best."
-Mufti Taqi Usmani
He mentions another hadith which relates that a dropped stone took 70 years to traverse the depths of Hell.
(translated from an oral lecture in Urdu)