Found this over at Catholic Answers...
There was a little old lady who every morning stepped onto the front porch, raised her arms to the sky and shouted "PRAISE THE LORD!"
One day an atheist moved into the house next door. He became irritated at the little old lady. Every morning he'd step onto his front porch after her and yell. "THERE IS NO LORD!" Time passed with the two of them carrying on in this way every day.
One morning, in the middle of winter, the little old lady stepped onto her front porch and shouted: "PRAISE THE LORD! Please Lord, I have no food and I am starving, provide for me oh Lord!" The next morning she stepped out onto her porch and there were two huge bags of groceries sitting there.
"PRAISE THE LORD!"she cried out. "HE HAS PROVIDED GROCERIES FOR ME!" The atheist neighbour jumped out of the hedges and shouted: "THERE IS NO LORD. I BOUGHT THOSE GROCERIES!!"
The little old lady threw her arms into the air and shouted: "PRAISE THE LORD! HE HAS PROVIDED ME WITH GROCERIES AND MADE THE DEVIL PAY FOR THEM!