Is it permissible to lie to donors to Muslims, when each of them insists on donating for one specific thing, and then to give the donation of one of them to other Muslims?

It is not permissible to take a donor's money designated for a specific purpose and spend it on another purpose that contradicts what the donor stipulated, except with their permission. This is because doing so involves deception and a violation of the donor's condition. The scholars have stated that the condition of the waqif (endower) is like the text of the Lawgiver, as long as it does not contradict it.