"The Messenger of Allah said: 'The screen between the Jinn and the nakedness of the sons of Adam is that when a person enters the Kanif, he should say: Bismillah (in the name of Allah).'"
Sunan Ibn Majah Book 1, Hadith 31
← Previous Hadith "The Messenger of Allah said: 'These Hushush (waste areas) are visited (by devils), so when anyone of you enters, let him say: 'Allahumma inni a`udhu bika minal-khubthi wal-khaba'ith (O Allah, I seek refuge with You from male and female devils).'" (Sahih)

Other chains with similar wording.

Sunan Ibn Majah Book 1, Hadith 30 Next Hadith → "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).'"

Sunan Ibn Majah Book 1, Hadith 32