Four legs good, two legs bad.

George Orwell (1903–1950) English journalist, essayist, writer [pseud. of Eric Arthur Blair]

Animal Farm, ch. 3 (1945)
    (Source)

The "essential principle" of Animalism, as propounded by the character Snowball (summed up so the less intelligent animals don't have to memorize the Seven Commandments). It becomes the Spontaneous Demonstration mantra of the sheep.

Later, as the pigs co-opt the Revolution and begin to walk upright, the phrase changed to "Four legs good, two legs better!"