By Friedrich Engels
The link above goes (again) to the Kindle collection of works by Marx & Engels. But you can easily find Anti-Duehring by itself in both Kindle and print (sometimes listed as Anti-Dühring). This famous book, first published in 1878, is meant as a response to "Dr. Eugene Duehring, privat docent at Berlin University" (see translator's introduction), who publicly announced that he had "converted" to socialism but described a socialism different from Marx and Engels' vision. But Anti-Duehring has also been described as Engels' major work on Marxist theory. It was deeply influential to the young A.R. Luria as he developed his ideas of a Marxist psychology. Its last chapter was republished with some modifications as the pamphlet Socialism: Utopian and Scientific.
It's also hard to read. Not because it is especially challenging material—Engels didn't write especially challenging books, in my opinion—but because the tone is unrelentingly polemic and sarcastic. It's like reading a YouTube comments section.
It has often crossed my mind that the sneering, sniping style Engels uses here became the model for Lenin, who passed it on to Ilyenkov. (Stalin's style was less sneering and more autocratic, perhaps reflecting the two men's different political positions at the time they wrote their books.) I tend to read performative contempt as a compensation for weakness, so I had trouble evaluating the argument on its merits.
The argument itself, though, expands dialectic by applying it to the natural world and making it a natural law, just as Dialectics of Nature did. Engels argues, as Ilyenkov later did, that contradictions seem impossible in traditional logic because traditional logic doesn't take change into account (Ch.7): "motion is just the continuous establishing and dissolving the contradiction" [sic]. It is this argument, more fully developed in Dialectics of Nature, and the companion argument that religion will die a natural death, more fully developed in The Origin of the Family, Private Property, and the State, that make Anti-Duehring an important book. But those other books spare you the constant invective. I suggest reading them first.