What did the Founding Fathers really say? - Americans United

What religion were the Founding Fathers? Were they Deists? Were the founders evangelical Christians? The faith of the Founding Fathers is a fascinating and hotly debated subject. But their personal religious beliefs, while interesting, matter far less to the debates in which those beliefs are typically raised than the fact that nearly all the Founders cherished religious freedom and church-state separation…

https://www.au.org/what-did-the-founding-fathers-really-say/  

James Madison | The First Amendment Encyclopedia

The target of the pamphlet was a bill before the Virginia Assembly supported by Gov. Patrick Henry that would have laid a general tax to pay Christian teachers a modest salary. The bill would not have established any one denomination (all Christian churches were eligible for the funds), but it would have made Christianity the established religion of the state. 

Madison considered the bill a "dangerous abuse of power"; he reasoned that if government could establish Christianity over other religions, then it would also have the power to elevate one Christian group over another. Madison believed that religion was a matter of individual conscience and that giving legislators control over religious belief would inevitably lead to violation of other basic rights: "It is proper to take alarm at the first experiment on our liberties." Madison succeeded in defeating the religious assessment bill and then spearheaded passage, in 1786, of Thomas Jefferson's Virginia Statute for Religious Freedom...

https://www.mtsu.edu/first-amendment/article/1220/james-madison

Here are 5 founding fathers whose skepticism about Christianity would make them unelectable today - Raw Story

To hear the Religious Right tell it, men like George Washington, John Adams, Thomas Jefferson and James Madison were 18th-century versions of Jerry Falwell in powdered wigs and stockings. Nothing could be further from the truth. Unlike many of today's candidates, the founders didn't find it necessary to constantly wear religion on their sleeves. .....
https://www.rawstory.com/2018/06/5-founding-fathers-whose-skepticism-christianity-make-unelectable-today/