This comes from a nice blog I just discovered.
“The anarchists put the thing upside down. They declare that the proletariat revolution must begin by doing away with the political organization of the state. But after its victory the sole organization which the proletariat finds already in existence is precisely the state. This state may require very considerable alterations before it can fulfill its new functions. But to destroy it at such a moment would be to destroy the only organism by means of which the victorious proletariat can assert its newly conquered power, hold down its capitalist adversaries and carry out that economic revolution of society without which the whole victory must end in a new defeat and in a mass slaughter of the workers similar to those after the Paris Commune.”
– Frederick Engels, “Engels to Philipp Van Patten in New York,” London, April 18, 1883.