Mr. Darwin begs me to say that he receives so many letters that he cannot answer them all. He considers that the theory of evolution is quite compatible with the belief in a God; but that you must remember that different persons have different definitions of what they mean by God.
volume I, chapter VIII: "Religion", page 307; letter from Emma Darwin (wife) to N.A. Mengden (8 April 1879) - The Life and Letters of Charles Darwin (1887)