It is possible to imagine something more terrible than a hell of suffering, and that is a hell of boredom.

[On peut rêver quelque chose de plus terrible qu’un enfer où l’on souffre, c’est un enfer où l’on s’ennuierait.]

Victor Hugo (1802-1885) French writer

Les Misérables, Part 2 “Cosette,” Book 4 “The Gorbeau Tenement,” ch. 1 (2.4.1) (1862) [tr. Donougher (2013)]
    (Source)

See Fromm (1931).

(Source (French)). Alternate translations:

Something more terrible than a hell of suffering may be conceived; to wit, a hell of ennui.
[tr. Wilbour (1862)]

It is possible to imagine something more horrible than an Inferno in which people suffer; it is on in which they are bored.
[tr. Wraxall (1862)]

Something more terrible than a hell where one suffers may be imagined, and that is a hell where one is bored.
[tr. Hapgood (1887)]

It is possible to conceive of something even more terrible than a hell of suffering, and that is a hell of boredom.
[tr. Denny (1976)]

There is something more terrible than a hell of suffering -- a hell of boredom.
[tr. Wilbour/Fahnestock/MacAfee (1987)]

One can dream of something more terrible than a hell where one suffers; it’s a hell where one would get bored.
[E.g.]