Late in life, Rigdon recalled his response to the Book of Mormon when it was delivered to him:
“There was no man living so well qualified to judge of the divine authenticity of the book of Mormon as he was. His knowledge of the Lords manner of writing was such as enabled him to detect it when he saw it, & thus it was that he received the Book of Mormon when I the Lord sent it to him.”
From Copying Book A & Book of the revelations of Jesus Christ To The children of Zion Through Sidney Rigdon Prophet & Seer & Revelator. 1864.
Section 37 (Post Collection, U. Utah)