What is the ruling on greeting with "Salam" upon entering the mosque, and has Allah Almighty commanded us to do so? And is the raising of voices by worshippers in the mosque a sign of the Hour?

It is recommended for someone entering a mosque and passing by a group of people to offer greetings to them in a way that does not disturb those praying. This should be repeated for each group one passes by who did not hear the previous greeting, unless the mosque is large and full of people, in which case it is sufficient to greet upon entering and at one's prayer spot. However, if people are in a specific area and one does not pass by them upon entering, then one should perform the mosque greeting first, then go to them and greet them, based on the Prophet's (peace be upon him) saying: "Go back and pray, for you have not prayed," in the story of the one who prayed poorly.