Uthman bin Affan (Radhiallahu anhu) reported:
The Messenger of Allah (Sallallaahu 'alaihi wasallam) said:
"He who recites three times every morning and evening: `Bismillahil-ladhi la yadurru ma`as-mihi shai'un fil-ardi wa la fis-sama'i, wa Huwas-Sami`ul-`Alim (In the Name of Allah with Whose Name there is protection against every kind of harm in the earth or in the heaven, and He is the All-Hearing and All-Knowing),' nothing will harm him.''
[Abu Dawud and At-Tirmidhi]
Commentary: The prayer cited in this Hadith means that "I seek the Protection of Allah by means of which one can save himself from every vice, whether it is an animal or man, a jinn or Satan because He is Aware of everyone's condition and Capable of hearing everybody's petition. He who comes in His Protection none can harm him, except that which He wills.''
(Riyad-us-Saliheen - Hadith No. 1457)