Lenin - On Socialism in One Country https://marxistleninists.org/Reading%20Guide/Socialism%20in%20one%20country/index.htm
The Peasant War in Germany by Frederick Engels http://hiaw.org/defcon6/works/1850/peasant-war-germany/index.html
✊ The use of the fist as a salute by communists and antifascists is first evidenced in 1924, when it was adopted for the Communist Party of Germany's Roter Frontkämpferbund ("Alliance of Red Front-Fighters"). In reaction, the Nazi Party adopted the well-known Roman salute two years later. https://www.jstor.org/stable/27672022