not believe (your) ears

to be very surprised by something that someone tells you.

We couldn't believe our ears when we heard that our tickets weren't waiting for us at the airport ticket counter.

• a ball-breaker
• a ballpark estimate
• a ballpark figure
• a balls-up
• a banana republic
• a banana skin
• a Band-Aid
• a bang up job
• a baptism by fire
• a baptism of fire
• a bargaining chip
• a basket case
• a battle of nerves
• a battle of wills
• a battle of wits
• ABCs of
• ABCs of something
• a bean counter
• a bear hug
• a beast of burden
• a belly laugh
• a Bible-basher
• abide by
• abide by something
• a big ask