“The qualities of a good prosecutor are as elusive and as impossible to define as those which mark a gentleman. And those who need to be told would not understand it anyway. A sensitiveness to fair play and sportsmanship is perhaps the best protection against the abuse of power, and the citizen's safety lies in the prosecutor who tempers zeal with human kindness, who seeks truth and not victims, who serves the law and not factional purposes, and who approaches his task with humility.”

Polly Peachum, in Act 3, scene 1, p. 74
Variant translation: The law was made for one thing alone, for the exploitation of those who don't understand it, or are prevented by naked misery from obeying it.
The Threepenny Opera (1928)

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Variant: Believe those who seek the truth, doubt those who find it
Context: Believe those who seek the truth, doubt those who find it; doubt all, but do not doubt yourself.

Address at the Convocation of the University of British Columbia, May 18, 1954
Speaking Of Canada - (1959)

Source: Darkfever

Speech in New York, 1858.
1850s

Source: Professor Stewart's Cabinet of Mathematical Curiosities

Ainsi soit-il; ou, Les Jeux sont faits
So be it; or, The chips are down
Gallimard
1952
174
Original: (fr) Croyez ceux qui cherchent la vérité, doutez de ceux qui la trouvent; doutez de tout, mais ne doutez pas de vous-même.