Who said "Gratitude binds allies more firmly than contracts"?

This quote is attributed to Salvor Hardin.

Gratitude binds allies more firmly than contracts - Salvor Hardin

"Gratitude binds allies more firmly than contracts"

Salvor Hardin Gratitude

Character in Foundation

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"Violence is the last refuge of the incompetent"

"It is the chief characteristic of the religion of science that it works"

"Found a religion? It's the only way to keep them quiet"

"Violence is the last refuge of the incompetent"

"Gratitude makes life richer."

"A grateful heart is a happy heart."

"Respect those who came before us."

"Life's greatest treasures are the people we love"