حَدَّثَنَا عُبَيْدُ اللَّهِ بْنُ مُعَاذٍ، حَدَّثَنَا أَبِي، حَدَّثَنَا شُعْبَةُ، عَنْ عَبْدِ اللَّهِ بْنِ أَبِي السَّفَرِ، عَنِ الشَّعْبِيِّ، عَنْ خَارِجَةَ بْنِ الصَّلْتِ، عَنْ عَمِّهِ، أَنَّهُ مَرَّ بِقَوْمٍ فَأَتَوْهُ فَقَالُوا إِنَّكَ جِئْتَ مِنْ عِنْدِ هَذَا الرَّجُلِ بِخَيْرٍ فَارْقِ لَنَا هَذَا الرَّجُلَ ‏.‏ فَأَتَوْهُ بِرَجُلٍ مَعْتُوهٍ فِي الْقُيُودِ فَرَقَاهُ بِأُمِّ الْقُرْآنِ ثَلاَثَةَ أَيَّامٍ غُدْوَةً وَعَشِيَّةً كُلَّمَا خَتَمَهَا جَمَعَ بُزَاقَهُ ثُمَّ تَفَلَ فَكَأَنَّمَا أُنْشِطَ مِنْ عِقَالٍ فَأَعْطُوهُ شَيْئًا فَأَتَى النَّبِيَّ صلى الله عليه وسلم فَذَكَرَهُ لَهُ فَقَالَ النَّبِيُّ صلى الله عليه وسلم ‏"‏ كُلْ فَلَعَمْرِي لَمَنْ أَكَلَ بِرُقْيَةٍ بَاطِلٍ لَقَدْ أَكَلْتَ بِرُقْيَةٍ حَقٍّ ‏"‏ ‏.‏

Kharijah b. al-Salt quoted his paternal uncle as saying that he passed by a clan (of the Arab) who came to him and said: You have brought what is good from this man. Then they brought a lunatic in chains. He recited Surat al-Fatihah over him three days, morning and evening. When he finished, he collected his saliva and then spat it out, (he felt relief) as if he were set free from a bond. They gave him something (as wages). He then came to the Prophet (PBUH) and mentioned it to him. The Messenger of Allah (PBUH) said: Accept it, for by my life, some accept it for a worthless charm, but you have done so far a genuine one. Translation Not Available

Book reference: Sunan Abi Dawud Book 24 Hadith 3420
Web reference: Sunan Abi Dawud Book 23 Hadith 3413