Say this dua four times in the evening:

اَللَّهُمَّ إِنِّي أَمْسَيْتُ أُشْهِدُكَ، وَأُشْهِدُ حَمَلَةَ عَرْشِكَ، وَمَلَائِكَتِكَ، وَجَمِيعَ خَلْقِكَ، أَنَّكَ أَنْتَ اللَّهُ لَا إِلَهَ إِلاَّ أَنْتَ وَحْدَكَ لَا شَرِيكَ لَكَ، وَأَنَّ مُحَمَّدًا عَبْدُكَ وَرَسُولُكَ

Allaahumma 'innee 'amsaytu 'ush-hiduka wa 'ush-hidu hamalata 'arshika, wa malaa'ikatika wajamee'a khalqika, 'annaka 'AntAllahu laa 'ilaaha 'illaa 'Anta wahdaka laa shareeka laka, wa 'anna Muhammadan 'abduka wa Rasooluka.

O Allah, verily I have reached evening and call on You, the bearers of Your throne, Your angels, and all of Your creation to witness that You are Allah, none has the right to be worshipped except You, alone, without any partner and that Muhammad is Your Servant and Messenger. Allah will spare whoever says this four times in the morning or evening from the Hell-fire.

Reference: Hasan (Ibn Baz). Abu Dawud: 5069