Brother Anderson came into my office for a few minutes this morning. He said that President [Heber J.] Grant told him that Joseph F. Smith told President Grant about an informal, friendly conversation he had in Independence with Joseph Smith III [RLDS President]. Joseph Smith III leaned over to President Smith and said, "You know, I wish I knew for sure which one of us is right," and President Joseph F. replied, "I thank the Lord that I do know which one is right."
A close friend of Frederick M. Smith was Dr. Henry Russell. Dr. Russell told President Grant in the presence of Elder Anderson that he had said to Frederick M., "Do you mind if after you die I do your temple work for you?" President Smith hesitated a moment and said, "No, I guess that would be all right."
President Grant was talking with Frederick M. Smith one time and President Smith asked President Grant if he had ever seen the Lord. President Grant said no, but he had felt the presence of the Holy Spirit of the Lord after his call to be an apostle. At that time the Holy Spirit assured him that his call was from the Lord and after that experience he was reassured that he should be an apostle.
[Source: Confessions of a Mormon historian : the diaries of Leonard J. Arrington, 1971-1997, Gary James Bergera, editor, Signature Books, 2018]