“There is one thing stronger than all the armies in the world, and that is an idea whose time has come”

Variant: No force on earth can stop an idea whose time has come

Often attributed to Hugo as a paraphrase of a similar idea in his Histore d'un Crime (1877): "One resists the invasion of armies; one does not resist the invasion of ideas", the wording of this famous statement actually more closely resembles a passage from the relatively obscure Les Francs-Tireurs (1861) by Gustave Aimard, p. 68 https://books.google.com/books/about/Les_francs_tireurs.html?id=mKI4AQAAIAAJ:
Il y a quelque chose de plus puissant que la force brutale des baïonnettes: c'est l'idée dont le temps est venu et l'heure est sonnée.
There is something more powerful than the brute force of bayonets: it is the idea whose time has come and hour struck.
Translated into English as The Freebooters : A Story of the Texan War (1861) https://archive.org/details/freebootersstory00aima, p. 57, Ward & Lock edition
Misattributed
Variant: More powerful than the mighty armies is an idea whose time has come.

Source: War and Peace

The Dreamstone, Book One : The Gruagach, Ch. 1 : Of Fish and Fire
Arafel's Saga (1983)
Context: Men changed whatever they set hand to. They wrought their magic on beasts, to make them dull and patient. They brought fire and the reek of smoke to the dales. They brought lines and order to the curve of the hills. Most of all they brought the chill of iron, to sweep away the ancient shadows.
But they took the brightness too. It was inevitable, because that brightness was measured against that dark. Men piled stone on stone and made warm homes, and tamed some humbler, quieter things, but the darkest burrowed deep and the brightest went away, heartbroken.
Save one, whose patience or whose pride was more than all the rest.
So one place, one untouched place in all the world remained, a rather smallish forest near the sea and near humankind, keeping a time different than elsewhere.

Source: The Anarchist Cookbook (1971), Chapter One: "Drugs", p. 59.

On the decade which she fit in best, as quoted in Life and Lies of an Icon (1995) by Richard Witts.
Context: I would say the time has not yet come. I rebel against the present, whenever it is, because I have not seen any change, other than oppositions grow stronger. I would be a communist if it was more anarchist. Otherwise, I see only everything as an absurdity, so I can laugh and cry. I have lived in a continuation, from birth and growing towards death in a chain that cannot end. I don't see this decade then that decade. The same things happen in different guises. I am bohemian but at one time you would call me a hippie or a punk. I remain a bohemian whatever you call me. So maybe I am locked in the fifties. But I have never desired to grow up from my world as a child, which is when things are most clear and utopian. They are clear because you are at the center and you see all around you. When you get older you lose your sight … I lost something of my childishness when people around me start dying. Four of my family died within a year.

ibid, p: 116

Source: Written on the Body