Why do you believe?

[pocaracas]

I think you wanted to finish with "If all prayers work, you have evidence that disproves atheism." Otherwise, you fall into the coincidence well.

If it's just coincidence, then the prayer didn't work.

Ah, I see... I thought you were going for the "if it works once, it's coincidence".
So it needs to work a lot of times (ideally, always) for the coincidence factor to be negligible.