George A. Smith recalls being introduced to plural marriage in the summer of 1841.
George A. Smith, Letter to Joseph Smith III, October 9, 1869, MS 1322, Church History Library
I Returning <to Nauvoo> from this mission in July 1841, at which to Nauvoo, <at> One of the first interviews with your father he astonished me by teaching me the <I was greatly astonished at hearing from his lips> the doctrine of Patriarchal <plural> marriage which he continued to do <preach to me> from time to time up till <nearly> the day of his death. My last conversation with him on this subject being a few days previous to my departure with my the quorum <of the Twelve> on our mission to the Eastern States where we were at the time of his death with the exception of Elders Taylor & Richards who shared his dangers in Carthage jail.