Invocation for entering the mosque  
 

"أَعُوذُ بِاللهِ الْعَظِيمِ، وَبِوَجْهِهِ الْكَرِيمِ، وَسُلْطَانِهِ الْقَدِيمِ، مِنَ الشَّيْطَانِ الرَّجِيمِ". [بِسْمِ اللهِ، وَالصَّلَاةُ وَالسَّلَّامُ عَلَى رَسُولِ اللهِ] "اللَّهُمَّ افْتَحْ لِي أَبْوَابَ رَحْمَتِكَ".

20. 'A'oothu billaahil-'Adheem, wa bi-Wajhihil-Kareem, wa Sultaanihil-qadeem, minash-Shaytaanir-rajeem. [Bismillaahi, wassalaatu.] [Wassalaamu 'alaaRasoolillaahi.] Allaahum-maftah lee 'abwaaba rahmatika.

I seek refuge in Almighty Allah, by His Noble Face, by His primordial power, from Satan the outcast.¹ [In the Name of Allah, and blessings.]² [And peace be upon the Messenger of Allah.]³ O Allah, open before me the doors of Your mercy.⁴

Reference:
¹ Abu Dawud and Al-Albani, Sahihul-Jdmi' As-Saghir (Hadithno. 4591).
² Ibn As-Sunni (Hadith no. 88), graded good by Al-Albani.
³ Abu Dawud 1/126, see also Al-Albani, Sahihul-Jami'As-Saghir 1/528.
⁴Muslim 1/494. There is also a report in Sunan Ibn Majah on the authority of Fatimah (RA), : "O Allah, forgive me my sins and open for me the doors of Your mercy." It was graded authentic by Al-Albani due to supporting Ahadith. See Sahih Ibn Majah 1/128-9.