Sunan Abi Dawud Book 2, Hadith 76
I met ‘Uqbah b. Muslim and said to him: it has been reported to me that someone has narrated to you from the prophet (ﷺ) that when he entered the mosque, he would say: I seek refuge in Allah, the Magnificent, and in His noble face, and in his eternal domain, from the accursed Devil. He asked : is it so much only? I said: Yes. He said: when anyone says so. The devil says: he is protected from me all the day long.
when any of you enters the mosque he should invoke blessing on the prophet (ﷺ) and then he should say: O Allah, open to me the gates of thy mercy. And when he goes out, he should say: O Allah, I ask thee out of Thine abundance.
Abu Qatadah reported the Messenger of Allah (May peace be upon him) as saying; when any one of you enters the mosque, he should pray two RAKAHS before sitting down.