The other day at work I wanted to get a soda from the vending machine but didn't have enough money. I had finished lunch and was thirsty, so I started looking around the floor for a spare quarter. While doing that I decided to ask God if he'd give me a quarter so I could buy the soda. I looked around a little bit more and headed back to my desk thinking that God decided not to give me a quarter for a soda. No more than 10 minutes later did my coworker walk by my cubicle and say "Did anybody drop a quarter?" I jumped up and said, "Yes, I did, well I didn't but I'll take it!"
God gave me a quarter. Would he have had I not prayed? Maybe. Would I have known it was from Him had I not prayed? Maybe. In any event, if you ever question God's existence remember God's quarter.