"History as selective as this leads quickly to unreality. Before Mohammed there is blackness: slavery, exploitation. After Mohammed there is light: slavery and exploitation vanish. But did it? How can that be said or taught? What about all those slaves sent back from Sind to the caliph? What about the descendants of the African slaves who walk about Karachi? There is no adequate answer: so the faith begins to nullify or overlay the real world."
January 1, 1970
https://en.wikiquote.org/wiki/Slavery_in_India