…the laws and constitution of the people…I have suffered to be established, and should be maintained for the rights and protection of all flesh, according to just and holy principles;
That every man may act in doctrine and principle pertaining to futurity, according to the moral agencywhich I have given unto him, that every man may be accountable for his own sins in the day of judgment.
Therefore, it is not right that any man should be in bondage one to another.
And for this purpose have I established the Constitution of this land, by the hands of wise men whom I raised up unto this very purpose…
Original Source
Doctrine & Covenants 101:77-80
Revelation given to Joseph Smith the Prophet, at Kirtland, Ohio, December 16 and 17, 1833
https://www.lds.org/scriptures/dc-testament/dc/101.77-80?lang=eng
Accessed 15/5/2016