Never let your sense of morals prevent you from doing what is right!

Isaac Asimov (1920-1992) Russian-American author, polymath, biochemist

Foundation, Part 4 “The Traders,” ch. 1, epigraph (1951)
    (Source)

Motto of Salvor Hardin, as mentioned in the "Traders" entry in the Encyclopedia Galactica.

This part of the book was originally published as "The Wedge," Astounding Science-Fiction (1944-10), where the Salvor Hardin quote alone appears as the epigraph.