Uthman bin `Affan RadiyAllaahu 'Anhu reported: The Messenger of Allah (SallAllaahu 'Alayhi Wa Sallam) said, "He who recites three times every morning and evening:

بسم الله الذي لا يضر مع اسمه شيء في الأرض ولا في السماء وهو السميع العليم

[Bismillahil-lazhi 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.'' 


[Tirmidhi 3388, Hasan Sahih by Albani]