Affidavit from Joseph C. Kingsbury indicates he copied the plural marriage revelation on ca. July 15, 1843.
Joseph C. Kingsbury, Affidavit, March 7, 1870, in Affidavits about celestial marriage, 1869-1915 / Book number 2, 1870, 1903, MS 3423, CHL
Territory of Utah
County of Salt Lake } SS.
On this seventh day of March A. D. 1870 personally appeared before me, James Jack, a notary public in and for said county Joseph C. Kingsbury who was by me sworn in due form of law and upon his oath deposeth and saith, that on or about the fifteenth day of July A. D. 1843, in the city of Nauvoo, Hancock Co. State of Illinois, he wrote the Revelation on celestial or plural marriage from the mouth of Bishop Newel K. Whitney as he read from the original, which was in his possession just previous to its reported destruction by Emma Smith. And that the same, as published in the Deseret News Extra of September fourteenth 1852 is a true copy of the original. Joseph C. Kingsbury
Subscribed and Sworn to by the said Jos. C. Kingsbury the day and year first above written. }
James Jack
Notary Public