1- It is quoted from most Islamic scholars as follows: "they should recite the formula of endowment for a piece of land to make it as masjid, like (I endow it as masjid for the sake of Allah). However, according to the stronger view it suffices to make it a masjid if they build it as a masjid for the sake of Allah and a person say a prayer in it with the permission of the sponser.
2- De facto deed in endowing as a masjid is sufficient provided that his aim in construction is its construction/renovation as a masjid, specialy when one constructs a building on an ownerless piece of land. While if one has a house/shop, intends it to be a masjid and forces people to say their prayer there, it is problematic to suffice like that without reciting the formula of endowment deed.
3- After being built as a masjid it does not belong to a specific nationality, group, tribe, or individuals, and it is permissible for all Muslims to make use of it.
4- If it is not known that the masjid’s water is endowed to be used for wuḍū’ only by those who want to perform prayer, and in the masjid’s area the neighbors and passers-by usually use such water, there will be no problem in it, although observing caution in this regard is preferred.
5- One should avoid those acts which are not compatible with standing and prestige of a masjid like sport and related exercises.
6- There is no problem in having classes on Qur’an, practical laws of Islam, Islamic ethics and practicing religious and revolutionary songs in a masjid. But it is obligatory to show appropriate respect for the status, sacredness, and position of the masjid and it is impermissible to annoy and disturb the praying persons.
7- There is no problem in broadcasting the adhān in a usual and common way by means of a loudspeaker to announce the beginning of the time of prayer. But there is a problem in, broadcasting Qur’anic verses, supplication, and the likes using a loudspeaker in the masjid when it annoys the neighbors.
Ḥarām acts related to a masjid
8- It is ḥarām to make the ground,ceiling, wall, and roof of a masjid najis. If they become najis, one should purify them right away.
9- If a masjid is usurped, destroyed, abandoned and another building is constructed on its land or no sign of being masjid remained due to being abandoned and there is no hope for its renovation like in a case that there is no settlement/village in vicinity any more, it is not certain that it is ḥarām to make it najis.
10- Decorating a masjid with gold is ḥarām if it is considered as extravagance; otherwise, it is makrūh.
11- According to shar‘,non-Muslims should not enter Masjid al-Ḥarām. If their entrance to other masjids is considered to entail disgrace and disrespect to the sanctity of the masjid, it is, also impermissible; in general, they should not enter any masjid.
12- For a menstruating woman or if she is experiencing nifās ('bleeding after delivery') and a person in state of janābah, it is ḥarām to enter Masjid al-Ḥarām. It is also ḥarām for them to stay in other masjids. Rather, this rule is applied to their entering other masjids except for the following cases which are no problem: one passes through the masjid by entering from a door and exiting from another door or he/she wants to take something from the masjid. By obligatory caution, the same rules are applied to the shrines of the Infallible Imams (a). It is more compatible with caution to apply the rules of Masjid al-Ḥarām and those of Masjid al- Nabawī to these shrines.
Mustaḥabb acts of the masjid
13- It is mustaḥabb to build a masjid or renovate a masjid which is going to be destroyed. If it is destroyed in a way that it is impossible to repair it, they may destroy it completely to make a new one in its place. Rather, they may destroy a masjid which is in good conditions to replace it with a larger one to fulfill the people's need.
14- It is mustaḥabb to clean a masjid. For a person who wants to go to a masjid, it is mustaḥabb to wear perfume and good clean clothes, be careful that his shoes and feet are not dirty/impure, to enter the masjid sooner, and to exit later, than others, and at the time of entering/exiting the masjid to say dhikr and have humble heart.
15- It is mustaḥabb to say a two-rak'ah prayer as reverence and greeting to the masjid. In this regard, it suffices to say any other mustaḥabb/wājib prayer.
16- The merits of performing prayer in a masjid are applicable to women as well.
17- It is mustaḥabb to provide the masjid with light and to sweep it, to enter the masjid in a state of wuḍū’, and with the right foot and to exit the masjid with the left foot. Having enterd the masjid, it is mustaḥabb to face qiblah, to supplicate to Allah, to praise and thank Him and to recite salawāt.
18- It is mustaḥabb to say prayer in masjids. Rather it is makrūh not to go to a masjid without any excuse like raining, specially for the masjid's neighbours. It is narrated in a tradition: " there is no prayer for a neighbor of a masjids unless in the masjid". The most virtueous masjid is Masjid al-Ḥarām, then Masjid al-Nabawī, then Masjid Kūfeh, then Masjid al-Aqsā, then masjid jāmi', then masjid of one's tribe, and then the market masjid.
19- To build a masjid is among emphesized mustaḥabb acts and results in huge reward. It is narrated from the Holy Prophet (S.A.W): "Whoever build a masjid in this world, Allah will compensate for each span – or he said for each cubit – of it a city (as long as a distace to be covered during forty thousand years) of gold, silver, pearls, rubies, emeralds, aquamarines and beryls".
Makrūh acts of a masjid
20- The following acts are makrūh in a masjid: to sleep unless one has no other choice, to talk about worldly affairs, industrial works, to recite a poam unless it contains an advice or the like, to drop saliva, mucus from chest/nose, to shout and search for a lost person/property. However, there is no problem in saying adhān loudly in a masjid.
21- To allow a mad to enter a masjid is makrūh. It is makrūh for a person who has eaten onion/garlic or the like and his mouth smell bothers people to go to a masjid.
22- To abandon a masjid unused is makrūh. According to a tradition, the masjid is one of the three complainants who make a complain to Allah, the sublime, on the Ressurection, the second is a scholar among ignorants and the third the Holy Qor'an on which there is dust and is not recited. It is narrated that: "Whoever goes to a masjid will get ten rewards, ten faults will be removed from his acts, and is promoted ten grades for any step he walks to the masjid and returns".
23- To say dead prayer in a masjid other than Masjid al-Ḥarām is makrūh.