Brigham says that, as a prophet, he knows Black people are the children of Cain and "cannot bear rule in the priesthood."
Brigham Young, Speech, February 5, 1852, Church History Library
If there never was a prophet or apostle of Jesus Christ spoke it before, I tell you, this people that are commonly called Negroes are <the> children of old Cain. I know they are. I know that they cannot bear rule in the priesthood.