'I myself am not a Marxist.' --Karl Marx

Accusing Guesde and Lafargue of “revolutionary phrase-mongering” and of denying the value of reformist struggles, Marx made his famous remark that, if their politics represented Marxism, “ce qu'il y a de certain c'est que moi, je ne suis pas Marxiste” (“what is certain is that I myself am not a Marxist”). ^[5]

5. Ibid., p.11. Marx's famous remark, quoted by Engels in a letter to Eduard Bernstein, can be found in Marx and Engels, Werke, Vol. 35. p.388.

https://www.marxists.org/archive/marx/works/1880/05/parti-ouvrier.htm#n5