It was narrated from Abu Hurairah that:The Mesenger of Allah said: "When anyone of enters the mosque, let him send peace upon the Prophet, then let him say: 'Allahumma aftahli abwaba rahmatik (O Allah, open to me the gates of Your mercy).' And when he leaves, let him send peace upon the Prophet and say: 'Allahumma- simni minash-shaitanir-rajim (O Allah, protect me from the accursed Shaitan)

English translation · Sunan Ibn Majah