Ending his preface to the first edition of Das Kapital, Marx states the following:
“I welcome every opinion based on scientific criticism. As to the prejudices of so-called public opinion, to which I have never made concessions, now, as ever, my maxim is that of the great Florentine: ‘Segui il tuo corso, e lascia dire le genti.'” –Karl Marx, Capital: A Critique of Political Economy, trans. Ben Fowkes, ed. David Fernbach, Fowkes, and Ernest Mandel (New York: Penguin Classics, 1976), p. 93.
As the editors note, Marx actually altered Dante’s words for his own purposes. The original line, Purgatorio V 13, is as follows: “Vien dietro a me, a lasica dir le genti.”