ipse dixit

Etymology
Borrowed from,. Originally used by the followers of, who claimed this or that proposition to be uttered by himself. Extended during the Middle Ages to the statements of, and more famously used in such contexts.

Noun

 * 1)  A dogmatic and unproved proposition or dictum that is accepted solely on the authority of someone who is known to have asserted it.
 * 2) An authority who makes such an assertion.
 * 1) An authority who makes such an assertion.
 * 1) An authority who makes such an assertion.

Etymology
, originally used by Pythagoreans.