SAHIH BUKHARI

Volume 1, Book 4, Number 144:

Narrated by Anas
Whenever the Prophet went to answer the call of nature, he used to say, "Allah-umma inni a'udhu bika minal khubuthi wal khaba'ith i.e. O Allah, I seek Refuge with You from all offensive and wicked things (evil deeds and evil spirits)."