No. The words ...
"The spice must flow"
... don't appear in any of the original series novels. The expression appears to come from the 1984 film.
LISTEN TO ME!! The spice must flow... the spice has given me
accelerated evolution for four thousand years... it has enabled you to
live two hundred years... the spice helps make the sapho juice, which
gives the red-lipped mentats the ability to be living computers... the
secret side of spice... the water of life.
Possibly the closest we get in the book series is in Dune
“A certain amount of killing has always been an arm of business,” the
Baron said, “but a line has to be drawn somewhere. Someone must be
left to work the spice.”
Paul turned back to look at the Emperor, said: “When they permitted
you to mount your father’s throne, it was only on the assurance that
you’d keep the spice flowing. You’ve failed them, Majesty. Do you know
“Stop playing the fool,” Paul barked. “The Guild is like a village
beside a river. They need the water, but can only dip out what they
require. They cannot dam the river and control it, because that
focuses attention on what they take, it brings down eventual
destruction. The spice flow, that’s their river, and I have built a
dam. But my dam is such that you cannot destroy it without destroying