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Source:John Whitmer reaffirmed his written testimony of the plates - Messenger and Advocate 2:286-287
John Whitmer reaffirmed his testimony as printed in the Book of Mormon even after he left the Church
John Whitmer published his witness to the plates, and reaffirmed the written testimony of the Eight Witnesses published in the Book of Mormon:
It may not be amiss in this place, to give a statement to the world concerning the work of the Lord, as I have been a member of this church of Latter Day Saints from its beginning; to say that the book of Mormon is a revelation from God, I have no hesitancy; but with all confidence have signed my named to it as such; and I hope, that my patrons will indulge me in speaking freely on this subject, as I am about leaving the editorial department. Therefore I desire to testify to all that will come to the knowledge of this address; that I have most assuredly seen the plates from whence the book of Mormon is translated, and that I have handled these plates, and know of a surety that Joseph Smith, jr. has translated the book of Mormon by the gift and power of God, and in this thing the wisdom of the wise most assuredly has perished: therefore, know ye, O ye inhabitants of the earth, wherever this address may come, that I have in this thing freed my garments of your blood, whether you believe or disbelieve the statements of your unworthy friend and well-wisher.
- John Whitmer, "Address To the patrons of the Latter Day Saints' Messenger and Advocate," (March 1836) Latter Day Saints' Messenger and Advocate 2:286-287. (italics added)