Elizabeth Ann Whitmer Cowdery affirms that her husband, Oliver Cowdery, always matained his testimony in the BOM.
Elizabeth Ann Whitmer Cowdery, Letter to David Whitmer, March 8, 1887, in The Return 3, no. 5 (December 1892): 7
A LETTER FROM O. COWDERY'S WIFE
Southwest City, MO., March 8th, '87
Dear Brother David:—I, Elizabeth Cowdery, wife of Oliver Cowdery, do make the following statements: That my husband, Oliver Cowdery, bore his testimony to the truth and divine origin of the Book of Mormon, as one of the three witnesses of the Book of Mormon; as to his standing on doctrine he stood where he did when he preached the first sermon; that was preached in the last days in the Church of Christ in 1829, when the Bible and the Book of Mormon alone were the guide to the faith of the church. From the hour when the glorious vision of the Holy Messenger revealed to mortal eyes the hidden prophecies which God had promised his faithful followers should come forth in due time, until the moment when he passed away from earth. He always without one doubt or shudder of turning affirmed the divinity and truth of the Book of Mormon. "God's promises naver fail."
From Your Sister,
Elizabeth Cowdery.