Abraham H. Cannon recalls that Brigham told Lorenzo Snow that blacks couldn't hold priesthood through premortal actions.
Abraham Cannon Journal, October 1, 1890, in Edward Leo Lyman, ed. Candid Insights of a Mormon Apostle: The Diaries of Abraham H. Cannon, 1889–1895 (Salt Lake City: Signature Books, 2010), 140
Pres. Brigham Young once told Bro. Snow that the reason negroes could not receive the Priesthood was thorough the exercise of their own agency before they came to this earth. Cain and Abel were princes in the first estate and stood at the head of a vast body of spirits for whom they were to beget bodies. Cain knew this and in slaying Abel he realized he was doing injury to all who acknowledged him as a prince. Hence when Cain was cursed his subjects were given the privilege of selecting some other medium through which to be born, but rather than select another prince they decided to be born of Cain and become partakers of his curse. For this reason wherever negro blood exists it will at times show itself in the offspring, and not until all of Abel's royal family have received will the curse be raised from Cain's posterity.