Not believe your ears/eyes
Definition 1 of 1
Pro Tip 1/3Strong Surprise
Used when something is so surprising, it's hard to accept as true at first. 
I couldn't believe my eyes when I saw the dog riding a skateboard.
Pro Tip 2/3Emotional Impact
Conveys strong emotions, like shock or joy, often in response to unexpected events. 
He couldn't believe his ears when she said 'I love you' out of the blue.
Pro Tip 3/3Not Literal
The phrase is figurative, not meaning actual disbelief but expressing strong reaction. 
When the fireworks began, we couldn't believe our ears; the booms were so loud!