article of faith

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A very basic belief not to be doubted.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun A thing that is believed as a matter of faith.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun (Christianity) any of the sections into which a creed or other statement of doctrine is divided
• noun an unshakable belief in something without need for proof or evidence