Just to follow up my claim with an actual quote from Washington regarding political parties, this is from his farewell address (a copy can be found
here):
"However combinations or associations of the above description [political parties] may now and then answer popular ends, they are likely, in the course of time and things, to become potent engines, by which cunning, ambitious, and unprincipled men will be enabled to subvert the power of the people, and to usurp for themselves the reins of government; destroying afterwards the very engines, which have lifted them to unjust dominion."