What is the authenticity of the hadith that obligates seeking a neighbor's permission before raising a building's wall, and what is the Islamic legal ruling on expanding a mosque unnecessarily, expensively, and in a way that harms the neighbor?

It is not permissible to expand the mosque if it causes harm to neighbors, unless they agree or are compensated. However, if the expansion is necessary, it can be carried out forcibly against the neighbor. The jurists have agreed on the permissibility of acquiring a neighbor's land by force at fair value for expansion when necessary, citing the actions of the Companions in expanding the Grand Mosque. The hadith (definition) "And do not build so high as to block the wind from him except with his permission" is very weak and cannot be used as evidence. Scholars have differed on whether building that blocks light or wind from a neighbor should be prohibited. The preponderant opinion is that building should be prohibited if the neighbor will suffer genuine harm, otherwise not, due to the generality of the hadith "There should be no harm nor reciprocating harm." Based on this, the mosque administration is not required to seek permission from the homeowner to expand the mosque, and he has no right to prevent them, because it is not expected that he will be harmed by this expansion.