Willard Richards' account of Joseph's Discourse on subject of Spirit of Elias, Elijah, and Messiah.
Joseph Smith, Discourse, 10 March 1844, as Reported by Willard Richards, p. [30], The Joseph Smith Papers website, accessed August 2, 2021
Sunday March 10 1844 I attended meeting <A M> at the Stand— by the Temple and preached on the subject of the spirit of <Elias> Elijah. Elias & Mesiah clearly defini[n]g the offices of the 3 personages.