Is building another mosque close to an existing one, and thereby dividing the congregants, considered a bid'ah (innovation) and a division of the Ummah? What is the advice directed to one who does this, and is prayer permissible in this new mosque?

Islam came with the command for unity and harmony. Out of concern for this, scholars prohibited multiple Friday prayers in one city except out of necessity, such as a small mosque or the city's widespread geographical area. The majority of scholars consider it forbidden to have multiple Friday prayers in the same village unless there is a need, because the Prophet (peace be upon him) and his Rightly Guided Caliphs only established one Friday prayer in Medina and all other Islamic cities in the early days of Islam. This is also to foster cooperation in righteousness and piety, to establish the rituals of Islam, to promote unity and affection, and to deepen understanding of the religion.

Many texts in the Qur'an and Sunnah encourage unity and warn against division. Among these are Allah's saying: "And hold firmly to the rope of Allah all together and do not become divided," and His saying: "And do not be like those who became divided and differed after the clear proofs had come to them."

However, if there is a dire need to establish two or more Friday prayers in a town or a large neighborhood, then there is no harm in it, according to the soundest opinion of scholars. This could be if the town has widely dispersed areas and it is difficult for its people to gather in one mosque, or if the neighborhood is so vast that its residents cannot gather in a single mosque, as happened when Baghdad was built, where two Friday prayers were established.

If this applies to the multiplicity of Friday prayers, then preventing the establishment of two adjacent congregations on the same street is even more strongly prohibited. Scholars have stipulated that it is forbidden to build a mosque next to another mosque if that will harm the older mosque and lead to the dispersal of its congregants. If there is no intent to harm and no need, then there are two narrations from Imam Ahmad regarding the permissibility of building it. Sheikh al-Islam Ibn Taymiyyah preferred that it should not be built and must be demolished if built.

The advice is to work towards unifying the community, removing animosity and hatred among the mosque's people, and gathering for prayer in the mosque that was built first.