Yours is one of the few lives precious to mankind, and for the continuance of which every thinking man is solicitous. Bigots may be an exception.

Letter to Dr. Joseph Priestley (21 March 1801); published in The Life of Thomas Jefferson (1871) by Henry Stephens Randall, Vol. 2, p. 644; this seems to be the source of a misleading abbreviation: "[Christianity is] the most ... perverted system that ever shone on man".