Mufti-e-Azam Hadhrat Maulana Muhammad Shafi’ Usmani (Rahimullah) writes the following chapter in his Tafseer “Maa’riful Qur’an”: Scholars have named fifteen items as etiquettes of the mosques. They are:
On entering the mosque one should greet the people already sitting there, with salam and if there is no one then say ‘Assalamu ‘Alayna Wa ‘Ala Ibadallahi-Saliheen’(but this is required when those present in the mosque are not offering their extra prayer or reciting Qur’an. If they are busy in any of these acts, then he should not greet them.)
After getting in the mosque one should offer two Rak’ats as tahiyyah tul-masjid. (This is required at a time when offering prayers is not prohibited, that is the time of sun rise, sun set or when sun is directly overhead.)
Should not carry out any transactions of sale or purchase in the mosque.
Should not carry any weapons in the mosque.
Should not make an announcement for the search for any of his lost items.
Should not raise his voice in the mosque.
Should not discuss worldly affairs in the mosque.
Should not quarrel with any one in the mosque.
Should not try to force his way into a row where there is no room.
Should not cross over in front of someone offering prayer.
Should avoid spitting or blowing of nose in the mosque.
Should not crackle fingers in the mosque.
Should not play with any part of the body.
Should keep clean of any filth, and should not take a baby or an insane along in the mosque.
Should keep busy in remembrance of Allah abundantly.
After listing these fifteen etiquettes Qurtubi has remarked that whoever has fulfilled these requirements has done justice with the mosque, and it has become a place of charm and security for him.
I have written a booklet on etiquettes and formalities of mosques under the title “Adaab-e-Masjid” (in Urdu). Anyone interested in the subject can consult it.