The Messenger of Allah (ﷺ), used to say when he entered the mosque:

بِسْمِ اللَّهِ اَللَّهُمَّ صَلِّ عَلَى مُحَمَّدٍ، اَللَّهُمَّ افْتَحْ لِي أَبْوَابَ رَحْمَتِكَ

Bismillaahi, Allaahumma salli 'ala muhammad, Allaahummaf ta'hlii abwaba ra'hmatik

In the Name of Allah, Ya Allah please send blessings and peace upon the Messenger of Allah (ﷺ). O Allah, open before me the doors of Your mercy.

Reference: Hasan (Albani). Ibn Sunni: 88, Muslim: 713