I recently heard this story in a sermon by Tim Keller. It is a fictional story, so don't go looking for it in the Bible. The story is by Elizabeth Elliott, though I'm not sure of the original title.
One day, Jesus instructed His disciples to find a stone to pick up and carry with them as they walked the road together. Peter, in particular, responds by selecting the smallest stone he can find, and he carries it as they journey. Eventually, Jesus and His disciples become hungry, but they have no food.
Jesus has the disciples stop by the road, and He says to them, "Now take out your stones."
As they bring out their stones, Jesus turns the stones into bread and invites them to eat. By now, Peter is regretting his choice of stone. He looks at his stone turned bread, and it's just a little crumb. He eats it, grumbling to himself, and afterward he is still quite hungry.
After lunch, Jesus tells His disciples to go find another stone to carry. This time, Peter goes and finds the largest stone he is able to bear. As they walk, he can barely carry the thing, but he can hardly wait until supper.
Finally, about supper time, hungry and exhausted, Jesus and His disciples reach a river side. As they are standing on the bank, Jesus once again asks them to take out their stones.
"Cast your stones into the river," He says. "Now follow Me."
The disciples obey, but they are perplexed by this command. Peter is a bit angry. This isn't what he or any of them were expecting.
In response to their frustration, Jesus simply asks, "Who were you carrying the stones for?"