Abu Dawud Book 22, Hadith Number 3892.
Chapter : Not known.
Narated By Alaqah ibn Sahar at-Tamimi : We proceeded from the Apostle of Allah (PBUH) and came to a clan of the Arabs.
They said: We have been told that you have brought what is good from this man. Have you any medicine or a charm, for we have a lunatic in chains?
We said: Yes. Then they brought a lunatic in chains. He said: I recited Surat al-Fatihah over him for three days, morning and evening. Whenever I finished it, I would collect my saliva and spit it out, and he seemed as if he were set free from a bond. He said: They gave me some payment, but I said: No, not until I ask the Apostle of Allah (PBUH).
He (the Prophet) said: Accept it, for, by my life, some accept it for a worthless charm, but you have done so for a genuine one.