Article 11 of the treaty of Tripoli:

"Art. 11. As the Government of the United States of America is not, in any sense, founded on the Christian religion; as it has in itself no character of enmity against the laws, religion, or tranquility, of Mussulmen (Muslims); and as the said States never entered into any war or act of hostility against any Mahometan (Mohammedan) nation, it is declared by the parties that no pretext arising from religious opinions shall ever produce an interruption of the harmony existing between the two countries."

(From Wikipedia).