"The bosom of America," he [Washington] declared a few months later, was "open to receive … the oppressed and persecuted of all Nations and Religions; whom we shall welcome to a participation of all our rights and privileges … if they are good workmen, they may be of Asia, Africa, or Europe. They may be Mohometans, Jews or Christians of any Sect, or they may be Atheists.
George Washington, quoted in Paul Boller’s George Washington and Religion
This is not as direct a source as I would like. I hope the quote is good, but I confess some doubts when I see Washington including atheists in it.