Marx & Engels collected works. Volume 48, Frederick Engels : Letters January 1887-July 1890
MLA
Marx, Karl, and Friedrich Engels. Marx & Engels Collected Works. London [England]: Lawrence & Wishart, 2001
APA, 7th edition
Marx, K., & Engels, F. (2001). Marx & Engels collected works. London [England]: Lawrence & Wishart
Chicago, 17th edition
Marx, Karl, and Friedrich Engels. Marx & Engels collected works. London [England]: Lawrence & Wishart, 2001