Why not buy a new plot of land to build a more spacious mosque, while retaining the old plot and using it to build a school or institute, instead of selling the old mosque that has become too small for its congregants?

Thank you for your question, which highlights important points.

First, the matter of uniting the Muslim community and keeping them in one mosque is a legitimate and commendable objective, as disunity leads to weakness and failure, as Allah Almighty says: ﴾And do not dispute, lest you lose courage and your strength depart.﴿ [Al-Anfal: 46].

Therefore, if the current mosque is sufficient for the needs of the Muslim community in that city, then it is not permissible for anyone to build another mosque next to it, because this would lead to dividing the community and creating dissension among them. This is the opinion of the Hanbali school of thought, and it is a strong opinion.

However, if the current mosque is not sufficient for the needs of the community, or if it is far from some neighborhoods, and there is a need for another mosque, then it is permissible to build another mosque. But even in this case, it is still better to try to expand the existing mosque first, if possible, before building a new one.

Second, regarding the issue of using the land of the first mosque for a school or institute, while the new mosque will contain the necessary facilities, this is a matter that needs to be considered in light of the specific circumstances. If the first mosque is no longer suitable for prayer due to its small size or other reasons, and there is a need for a larger mosque, then it is permissible to convert the old mosque into a school or institute, as long as this serves the interests of the Muslim community.

However, if the first mosque is still suitable for prayer, and there is no pressing need for a new mosque, then it is not permissible to convert it into a school or institute, because a mosque is primarily for prayer, and it should not be diverted from its original purpose unless there is a legitimate reason.

Third, your point about the difference between Muslim-majority countries and non-Muslim countries is very important. Indeed, the application of Islamic rulings must take into account the specific context and circumstances. What might be appropriate in a Muslim-majority country might not be appropriate in a non-Muslim country, where Muslims are a minority.

In non-Muslim countries, Muslims face unique challenges, and they need to be united and strong to preserve their identity and practice their religion. Therefore, any decision regarding the construction of mosques or other Islamic centers must take into account the need to strengthen the Muslim community and avoid anything that might lead to disunity or weakness.

In conclusion, I advise you to consult with the scholars and imams in your city, and to seek their guidance on this matter. They are more knowledgeable about the specific circumstances of your community, and they can provide you with the best advice. And Allah knows best.