Hadith: Those privies are attended by the devils, so if anyone of you goes to a privy, let him say: I seek refuge with Allah from the male and female devils

عن زيد بن أرقم رضي الله عنه ، عن رسول الله صلى الله عليه وسلم قال:«إنَّ هذه الحُشُوشَ مُحْتَضَرَةٌ، فإذا أتى أحدُكم الخَلَاءَ فَلْيَقُلْ: أعوذُ باللهِ مِنَ الخُبُثِ والخَبَائث».
[صحيح] - [رواه أبو داود وابن ماجه وأحمد]

Zayd ibn Arqam (may Allah be pleased with him) reported that the Messenger of Allah (may Allah's peace and blessings be upon him) said: "Those privies are attended by the devils, so if anyone of you goes to a privy, let him say: I seek refuge with Allah from the male and female devils."
Sahih/Authentic. - [Ibn Maajah]

Explanation

The place where one relieves himself (privy) is attended by the Jinn and the devils who wait there to inflict harm and trouble on humans. A privy is a place where one's private parts are uncovered, and the name of Allah is not mentioned. So, when a Muslim goes there, he should say this supplication: I seek refuge with Allah from the males and females from among the devils.