Asking religious people to prove the existence of god is like asking an atheist to disprove there being any intelligence in our design.
There's a huge difference between those two things.
Atheists/agnostics do not claim that there is no intelligence in our "design." They just point out the fallacy of coming to a conclusion that something exists when there is no evidence to support that conclusion. You can't prove a negative. Either you have evidence of something or you don't.
Faith is not evidence. Warm and fuzzy stories are not evidence. An old book is not evidence.