believe one's ears

Also, believe one's eyes. Trust one's own hearing or sight, as in We couldn't believe our ears when we heard that Gene was accepted at Stanford, or I couldn't believe my own eyes when the movie stars walked in. This expression of incredulity is nearly always stated negatively, as in the examples. [Early 1600s]

The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.