Niether Jefferson, nor Madison, nor Washington were Deists. Jefferson was a nominal Christian, who disbelieved the miraculous but attempted to pattern his life after the life of Christ and the teachings of the Bible. He believed in personal God who could intervene on behalf of humanity. Deists did not.
Washington was a Christian. A true believer. His writings make this abundantly clear.
Like I stated earlier, some founders were Deists. Most were not.
To be honest, there seems to be some disagreement on who was or was not a Deist, but the point doesn't interest me. The point that interests me is that these men (Deists or otherwise in their personal life) clearly believed in separation of church and state, and two of them (Jefferson and Madison) were primarily responsible for the First Amendment itself.