"Evil Wants Good to Prevail" by Paulo Coelho, Like the Flowing River

One day, the Persian poet, Rumi que Mo'avia, the first of the Ommiad caliphs, was sleeping in his palace when he was woken up by a strange man.
"Who are you?" he asked.
"I am Lucifer," came the reply.
"And what do you want?"
"It is the hour for prayers, and yet you are still asleep."
Mo'avia was amazed. Why was the Prince of Darkness, who seeks out the souls of men of little faith, reminding him to fulfil his religious duties?
"Remember," Lucifer explained, "I was brought up as an angel of light. Despite everything that has happened to me, I cannot forget my origins. A man may travel to Rome or to Jerusalem, but he always carries the values of his own country in his heart. Well, the same thing happens with me. I still love the Creator, who nourished me when I was young and taught me to do good. When I rebelled against Him, it was not because I did not love Him; on the contrary, I loved Him so much that I felt jealous when He created Adam. At that moment, I wanted to defy the Lord, and that was my downfall; nevertheless, I still remember the blessings bestowed on me and hope that, perhaps, by doing good, I can one day return to paradise."
Mo'avia replied: "I can't believe what you're saying. You have been responsible for the destruction of many people on earth."
"Well, you SHOULD believe it," insisted Lucifer. "Only God can build and destroy, because He is all-powerful. When He created man, He also created, as part of life, desire, vengeance, compassion, and fear. So when you look at the evil around you, don't blame me; I merely reflect back the bad things that happen."
Mo'avia was sure that something was wrong, and he began to pray desperately to God to enlighten him. He spent the whole night talking and arguing with Lucifer; but despite the brilliant arguments he heard, he remained unconvinced.
When day was dawning, Lucifer finally gave in and said:

"You're right. When I came yesterday to wake you up so that you would not miss the hour of prayer, my intention was not to bring you closer to the Divine Light. I knew that if you failed to fulfil your obligations, you would feel profoundly sad and, over the next few days, would pray with twice the faith, asking forgiveness for having forgotten the correct ritual. In the eyes of God, each one of those prayers made with love and repentance would be equivalent to two hundred prayers said in an ordinary, automatic way. You would end up more purified and more inspired; God would love you more; and I would be still further from your soul."

Lucifer vanished, and an angel of light took his place:

"Never forget today's lesson," the angel said to Mo'avia. "Sometimes evil comes disguised as an emissary of good, but its real intention is to cause more destruction."

On that day, and the days that followed, Mo'avia prayed with repentance, compassion, and faith. His prayers were heard a thousand times by God.