Joseph Lee Robinson recalls JS telling him about an angel with a sword commanding he restore plural marriage.
Joseph Lee Robinson, "History of Joseph Lee Robinson," in The Journal of Joseph Lee Robinson, ed. Oliver Preston Robinson and Mary Robinson Egan (n.p., 2003), 43–44
The prophet knew it would not avail anything to contend with the sisters. Said he, I will have to take that saying back and leave it as though there had been nothing said. For he was aware it was a very large pill for them or the people to swallow. But, as the Lord had revealed the principle of plural marriage to him and had informed him that the time had fully come that that doctrine should be taught and practiced by his people, the Latter-day Saints, as it was a very important item pertaining to the fullness of the gospel. He deemed it wisdom to throw out something for the people to reflect upon that they might begin to digest that very important doctrine which belongs to the dispensation of the fullness of times. But prior to this, he had besought the Lord to take this instruction from him that he might not have the responsibility of introducing and putting into practice that order of things because of the great opposition it would meet because of the traditions of the people.
But it came to pass the Lord instead of releasing him from that burden, he sent an holy angel with a drawn sword unto him, saying unto him, Joseph, unless you go to and immediately teach that principle (namely polygamy or plural marriage) and put the same in practice, that he, Joseph, should be slain for thus saith the Lord, that the time has now come that I will raise up seed unto me as I spoke by my servant Jacob as is recorded in the Book of Mormon, therefore, I command my people.
Brian C. Hales explains the dating of this account thus: "Robinson places this quotation in 1841 of his autobiography. Lawrence Foster dates this account to 1846. It appears the actual entry was written 1853 when the autobiographical recollections end and daily journal entries begin. It could be that in 1853 Robinson was copying from a previously recorded 1841 or 1846 entry in his journal, a journal that is not currently available. Dating this earlier than 1853 seems unwise." (Brian C. Hales, "Encouraging Joseph Smith to Practice Plural Marriage: The Accounts of the Angel with a Drawn Sword," Mormon Historical Studies 11, no. 2 [Fall 2010]: 71n1.)