The last two surahs of the Qur'an, Surat Al-Falaq and Surat An-Nas. These two surahs were sometimes regarded as "spell" or "charm" surahs which Muslims recite to protect themselves against evil spirits, curses, or when they are afraid.
Narrated Abdullah ibn Mas'udIt is said that some Jews cast spells on Muhammad, and these surahs were revealed for him to break the spell.
The Prophet of Allah disliked ten things: Yellow colouring, meaning khaluq, dyeing grey hair, trailing the lower garment, wearing a gold signet-ring, a woman decking herself before people who are not within the prohibited degrees, throwing dice, using spells except with the Mu'awwidhatan, wearing amulets, withdrawing the penis before the semen is discharged, in the case of a woman who is wife or not a wife, and having intercourse with a woman who is suckling a child; but he did not declare them to be prohibited. (Hadith - Abu Dawud)
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According to hadith reports, in the codex of `Abdullah ibn Masud, these two surahs were not included in his Qur'an collection as canonical. This have caused various rationalizations among Muslim scholars. For more details, see " THE COLLECTION OF THE QUR'AN -- from the hadiths, Section 5.3"