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