HCC cites JS as maintaining plural marriage is required for eternal life.
Horace C. Cummings, "Conspiracy of Nauvoo," The Contributor 5, no. 7 (1884): 259
They accuse me of polygamy, and of being a false Prophet, and many other things which I do not now remember; but I am no false Prophet; I am no impostor; I have had no dark revelations; I have had no revelations from the devil; I made no revelations; I have got nothing up of myself. The same God that has thus far dictated me and directed me and strengthened me in this work, gave me this revelation and commandment on celestial and plural marriage, and the same God commanded me to obey it. He said to me that unless I accepted it and introduced it, and practiced it, I, together with my people, would be damned and cut off from this time henceforth. And they say if I do so, they will kill me ! Oh, what shall I do? If I do not practice it, I shall be damned with my people. If I do teach it, and practice it, and urge it, they say they will kill me, and I know they will. But," said he, "we have got to observe it. It is an eternal principle and was given by way of commandment and not by way of instruction."