Authentic Supplication Number 068.

Upon entrance to the Masjid, The Messenger of Allah  would say Bismillah, 'allahumma salli `ala muhammad (82), and upon leaving he would say Bismillah, 'allahumma salli `ala muhammad.

Footnotes.
(82) In The Name of Allah. O' my 'ilah bestow grace, and peace upon Muhammad.

Reporters.
Al-Albani said that this was a comely hadeeth reported by Ibn As-Sunni (#86) with a chain of ascription that was said to be weak by Al-hafith Ibn Hajar in Takhreej 'al-'Adhkar; however, the hadeeth has testimonial Fatimah's hadeeth reported by Ibn As-Sunni, and At-Tirmithi who said it was comely. Al-Albani included this hadeeth in The Authentic of Good Sayings as #48.