not believe (one's) eyes
To be shocked or surprised by what one is seeing or has seen. Oh, I can't believe my eyes! Are you really throwing the ball in the house right now? Did you really buy me a new car? I don't believe my eyes!
not beˌlieve your ˈeyes/ˈears
(usually used with can’t or couldn’t) think that something you see/hear is very surprising: I couldn’t believe my ears when I heard my name mentioned on the radio.