What is the ruling on uttering the greeting of peace aloud upon entering the mosque during prayer?

The Sunnah for someone who enters the mosque and finds people praying in congregation is to join them and not to greet anyone. However, if one enters the mosque outside of prayer times, then it is Sunnah to begin with the two rak'ahs of greeting the mosque, and then to greet whomever one wishes. One should raise their voice with the greeting so that the greeted person can hear it, without exaggeration that would cause disturbance. The Sunnah indicates the permissibility of greeting someone who is praying and that they respond by gesturing. This does not contradict the hadith: "Indeed, prayer occupies one fully," because the general is carried by the specific. If it is permissible to greet someone who is praying, then greeting someone who is not praying in their presence is even more permissible.