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