George Muller had the gift of faith that's found in 1 Corinthians 12:9. If you want to see faith in action, journey thought the life of George Muller in his autobiography. The challenge the book hints at is this: "If this were a scientific experiment, can you duplicate it?"
This book was given to me as a gift. After having read it, I've bought copies to give away. It's truly hard to describe the impact this book made on me. In talking to others that have read it, I get the impression they were impacted as strongly as I was. It is an absolute game changer (In a good way) for one's prayer life and faith.