W. W. Phelps includes text of alleged revelation from Joseph.
Revelation, July 17, 1831, in W.W. Phelps, Letter to Brigham Young, August 12, 1861, MS 4583, Church History Library
Verily, I say unto you, that the wisdom of man in his fallen state, knoweth not the purpose and the privilege of my Holy Priesthood, but ye shall know when ye receive a fulness by reason of the anointing: For it is my will, in time, ye should take unto you wives of the Lamanites and Nephites, that their posterity may become white, delightsome and just; for even now their females are more virtuous than the gentiles.