In Mordenkainen’s Tome of Foes (p. 10), it is stated that Asmodeus’ Ruby Rod binds all devils to the letter of the law of their contracts. Failure of a devil to keep their end of the bargain in a contract would subject them to an inescapable punishment, but the nature of the punishment is not elaborated upon. I assume it’d be something ironic and debilitating.
The [Ruby Rod]…grants him and his underlings the right to enter into contracts with mortals for their souls but unleashes an inescapable punishment upon any devil that breaches such a contract.
Is there any official clarification on the nature of the punishment? If an answer is not available in 5e, I will accept an answer from other editions.