Abraham Lincoln said...
whether it be competent for me, as Commander in Chief of the Army and Navy, to declare the slaves of any State or States free, and whether at any time, in any case, it shall have become a necessity indispensable to the maintenance of the Government to exercise such supposed power, are questions which, under my responsibility, I reserve to myself
Context
Proclamation 90—Revoking Major General David Hunter's Order of Military Emancipation
05/18/1862