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Source:Rigdon:Manuscript found:in all of my intimacy with Joseph Smith he never told me but one story
Sidney Rigdon: "in all of my intimacy with Joseph Smith he never told me but one story"
Sidney Rigdon to his son John, just prior to Sidney's death, asserted that the Book of Mormon was true:
My father, after I had finished saying what I have repeated above, looked at me a moment, raised his hand above his head and slowly said, with tears glistening in his eyes: "My son, I can swear before high heaven that what I have told you about the origin of [the Book of Mormon] is true. Your mother and sister, Mrs. Athalia Robinson, were present when that book was handed to me in Mentor, Ohio, and all I ever knew about the origin of [the Book of Mormon] was what Parley P. Pratt, Oliver Cowdery, Joseph Smith and the witnesses who claimed they saw the plates have told me, and in all of my intimacy with Joseph Smith he never told me but one story. 
- Rex C. Reeve, Jr. "What is 'Manuscript Found'?" in Manuscript Found: The Complete Original "Spaulding" Manuscript, edited by Kent B. Jackson, Vol. 11 in the Specialized Monographs Series (Religious Studies Center, Brigham Young University, 1996), footnote 47.