DUA WHEN ENTERING THE MASJID

اَعُوْذُ بِاللّٰهِ الْعَظِيْمِ وَبِوَجْههِ الْكَرِيْمِ وَسُلْطَانِهِ الْقَدِيْمِ مِنَ الشَّيْطَانِ الْرَّجِيْمِ

I SEEK PROTECTION FROM ALLAH THE GREAT, AND FROM HIS KIND/GENEROUS BEING, AND FROM HIS KINGDOM THAT WILL NEVER END, FROM THE ACCURSED SHAYTAAN.  

After entering the Masjid recite Durood Sharif and thereafter recite,

اَللّٰهُمَّ اِفْتَحْ لِىْ اَبْوَابَ رَحْمَتِكَ

O Allah, open the doors of mercy upon me.