No person except a natural born Citizen, or a Citizen of the United States, at the time of the Adoption of this Constitution, shall be eligible to the Office of President; neither shall any Person be eligible to that Office who shall not have attained to the Age of thirty-five Years, and been fourteen Years a Resident within the United States.
Yep. Nowhere does it say anything that the President has to be a Christian. Nowhere does it say the President can't be a Muslim. Nowhere does it say the President can't be an atheist.
Article 2, Section 1, Clause 8:
"I do solemnly swear (or affirm) that I will faithfully execute the Office of President of the United States, and will to the best of my ability, preserve, protect and defend the Constitution of the United States."
No mention of God or any religion. No mention of any bibles or anything. This is the presidential oath.