Before entering the bathroom

[Bismillāhi] Allāhumma 'innī 'a`ūdhu bika minal-khubthi walkhabā'ith.

[In the Name of Allah]. O Allah, I seek protection in You from evil and the evil ones (or, from the evil male and female Jinn).

[ Al-Bukhari 1/45, Muslim 1/283. The addition of Bismillah at its beginning was reported by Said bin Mansur. See Fathul-Bari 1/244. Hisn al-Muslim 10 ]