If some hadiths are combined, the Dua for entering the mosque will be as follows:

أَعُوْذُ بِاللَّهِ الْعَظِيمِ وَبِوَجْهِهِ الْكَرِيمِ وَسُلْطَانِهِ الْقَدِيْمِ مِنَ الشَّيْطَانِ الرَّجِيْمِ، بِسْمِ اللَّهِ وَالصَّلَاةُ وَالسَّلَامُ عَلَى رَسُوْلِ اللَّهِ اَللَّهُمَّ افْتَحْ لِي أَبْوَابَ رَحْمَتِكَ

A'oodhu billahil-Aatheem wa bi wajhihil-kareem wa sultanihil-qadeem minash-shaytanir-rajeem, bismil-lahi, wassalatu wassalamu 'Aala rasoolil-lah, Allaahumma iftah lee abwaaba rahmatik

I take refuge with Allah, The Supreme and with His Noble Face, and His eternal authority from the accursed devil. In the name of Allah, and prayers and peace be upon the Messenger of Allah (ﷺ). O Allah, open the gates of Your mercy for me.

Reference: Sahih (Albani). Abu Dawud: 465, 466