In origin, when a Muslim meets another Muslim, they should greet them with Salaam. This applies to the Masjid or anywhere else they meet.
However, the Masjid has a specific ruling. It is not permitted for a Muslim to raise his/her voice in the Masjid, irrespective of whether they are reciting the Quran or greeting with Salam.Some people - Allah Guide them - when they enter the Masjid they enter with clamour. They might enter the Masjid whilst remembering in a loud voice or enter whilst giving Salam in a loud voice whilst people are busy in worshipping Allah; reciting the Quran, making Dhikr or whilst others are praying.
There is no doubt that entering the Masjid in this manner and greeting people with a loud voice or perhaps remembering Allah in a loud voice and creating clamour as they enter the masjid - is a mistake.
The Prophet (Peace and Blessings of Allaah be upon him) forbade the Companions from raising their voices over one another when they were reciting the Quran.
Once he entered into the Masjid and he found them reciting the Quran and they were competing with one another in making their voices louder against one another. So he said, "Each one of you are conversing with their Lord, so do not compete with one another in raising your voices whilst reciting the Quran." Narrated by Abu Dawood, 1332; classed as saheeh by al-Albaani in Saheeh Abi Dawood, 1183.
This is a command from the Prophet, not to raise thier voices when reciting the Quran so how about a person who enters into the Masjid whilst greeting people?
So the Muslim when he enters into the Masjid, he should make his way to the row and there is no harm in him greeting another person that he meets that is close to him, greeting them in a normal voice. As for entering into the Masjid and greeting everyone in a loud voice, then this is not allowed and it is not befitting.
