It was narrated that Anas bin Malik said:
"Whenever the Messenger of Allah entered the toilet, he would say: 'A'udhu Billahi minal-khubthi wa'l-khaba'ith (I seek refuge with Allah from male and female devils).'"
English reference: Vol. 1, Book 1, Hadith 298
Arabic reference: Book 1, Hadith 315