We may employ artifice to deceive a rival, anything against our enemies.
Pour tromper un rival l'artifice est permis; on peut tout employer contres ses ennemis.
Original text (French)
Notes from Wikiquote
As quoted in Dictionary of Quotations from Ancient and Modern English and Foreign Sources (1899) by James Wood
Variants
To mislead a rival, deception is permissible; one may use all means against his enemies.