It is recommended to greet the masjid by praying two rak`ah, and it is disliked to sit before praying these two rak`ah, and this is prescribed at all times Sahih Muslim 714 a
Translation
Abu Qatada (a Companion of the Prophet) reported Allah's Messenger (ﷺ) as saying
When any one of you enters the mosque, he should observe two rak'ahs (of Nafl prayer) before sitting.