For your consideration, Jim Carroll, from V.I. Lenin, "The Attitude of the Workers' Party to Religion":

"The philosophical basis of Marxism, as Marx and Engels repeatedly declared, is dialectical materialism, which has fully taken over the historical traditions of eighteenth-century materialism in France and of Feuerbach (first half of the nineteenth century) in Germany—a materialism which is absolutely atheistic and positively hostile to all religion."

And the declaration of Engels that he specifically referred to to was "Anti-Dühring".