This was not a real historical punishment or judicial sentence. It comes from a 1944 essay contest.
In the spring of 1944, during World War II, a 16-year-old African American high school student in Columbus, Ohio, won a local essay contest asking students what should be done with Adolf Hitler after the war. Her winning, single-sentence response was:
"Put him in a black skin and let him live the rest of his life in America.