“All for one, one for all, that is our motto.”
Tous pour un, un pour tous, c'est notre devise
Variant: All for one and one for all.
Source: The Three Musketeers (1844), Ch. 9: D'Artagnan Shows Himself.
Original
Tous pour un, un pour tous, c’est notre devise.
Paroles de d'Artagnan
Les Trois Mousquetaires, 1844
Variant: Tous pour un, un pour tous
Source: The Three Musketeers
Help us to complete the source, original and additional information
Alexandre Dumas 123
French writer and dramatist, father of the homonym writer a… 1802–1870Related quotes

“Commerce with all nations, alliance with none, should be our motto.”
Letter to Thomas Lomax (12 March 1799) http://www.gutenberg.org/files/16783/16783-h/16783-h.htm#2H_4_0253|
1790s

As quoted in Hitler and Nazism (1961) by Louis Leo Snyder, p. 66
Other remarks

Mes avis sur vos relations avec les femmes sont aussi dans ce mot de chevalerie: Les servir toutes, n'en aimer qu'une.
Le lys dans la vallée (1836), translated by Katharine Prescott Wormeley, part II: First Love.

“The motto should not be: Forgive one another; rather, Understand one another.”
Anarchism and Other Essays (1910), The Tragedy of Woman’s Emancipation
“Never get involved. That's my motto. I hurt no one. And no one can hurt me.”
Variant: Don't trust anyone. Be a cold fish. I hurt no one. And no one can hurt me.
Source: Chinese Cinderella: The True Story of an Unwanted Daughter