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).'" (IT)
English reference (IT): Vol. 1, Book 1, Hadith 298 (IT)
Arabic reference (IT): Book 1, Hadith 315 (IT)