President Brigham Young's voice sounding as the Prophet Joseph Smith

During the August 8, 1844, conference in Nauvoo, six weeks after the martyrdom of Joseph Smith, the Saints gathered to determine the leadership of the Church. Sidney Rigdon addressed the congregation in the morning, presenting his claims to guardianship. Following his speech, Brigham Young, President of the Quorum of the Twelve, stood to address the Saints and provide instruction on the order of the Priesthood. Many in attendance—including William Lampard Watkins—reported a profound spiritual manifestation during this meeting, often referred to as the "mantle of the Prophet" falling on Brigham Young. Witnesses testified that as Brigham Young spoke, his voice, manner, and physical appearance were so remarkably similar to the late Prophet Joseph Smith that they were convinced by the Holy Ghost that he was the rightful leader appointed to carry on the work of God. William Lampard Watkins, who was seventeen at the time, later recorded this experience in his journal, noting that the darkness felt by the Saints was dispelled as Brigham Young was filled with the power of the Holy Ghost, allowing the congregation to hear the voice of the "true shepherd" speaking as Joseph had done. This event served as a critical turning point that united the Saints and confirmed their commitment to follow the Quorum of the Twelve.

Fuller account of this event (in the witness’s own words):

On the 5th of August 1844, a special meeting was appointed for the church to come together to hear what he had to say on the subject. The next day President Brigham Young arived in Nauvoo with some of the other apostles from a Mission to the Eastern States And Called a meet- ing and invited Sidney Rigdon to the Stand and in the presance of the assembled thousands of the Saints Said to Sidney Now if you have any thing to say you have the apertunity and you can take the stand[.] President young then arose and took the stand his face and Countinence having the apearanc[e] of Joseph his voice and words were the familiar voice and Words of our martered prophet so much so the Who[l]e Congregation was fully satisfied that the mantle of the Prophet Joseph had fallen on him and some of the saints realy Believed it was in reality