the cauldron of Hell
Buddhist term referring to the cauldron in Hell where sinners are boiled. Often used in the set phrase 地獄の釜の蓋も開く, meaning even Hell's cauldron lid opens (i.e., even the most unlikely things can happen).
They say even the lid of Hell's cauldron opens, so maybe there will be a day when he isn't late.
Compound of 地獄 (Hell) + の (possessive particle) + 釜 (cauldron). The phrase originates from Buddhist depictions of Hell.