Is it permissible to sell land designated for building a mosque, given that there is a sufficient mosque nearby, and then use part of the profit from the sale to help a poor brother and his family?

If land was endowed or purchased with endowed money for building a mosque, and then it became no longer needed, it would be sold and its price spent on another mosque. If the money increased and no other mosque was found, it would be spent on public welfare and the poor. However, if the land was not endowed for a mosque, but rather came from general charities, then its price may be spent on the poor. The principle is that endowed money is spent on what it was endowed for. If it becomes impossible to benefit from it or it is no longer needed, it is then spent on something similar.