Before entering

بِسْمِ اللَّهِ

In the Name of Allah.

Bismillaahi

Then

اللَّهُمَّ إِنِّي أَعُوذُ بِكَ مِنَ الْخُبْثِ وَالْخَبَائِثِ

O Allah, I seek protection in You from the male and female unclean spirits.

Allaahumma 'innee 'a'oothu bika minal-khubthi walkhabaa'ith.

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