He—may Allah have mercy on him—was asked:

Concerning a man who said during his illness, “When I die, my house shall be an endowment for such-and-such a mosque.” He then recovered and subsequently incurred debts. Is this endowment valid and binding or not?

He answered:

He may sell the house to repay his debt, even if making the endowment conditional upon his death is valid, as scholars hold in one of their two views. This is no more binding than stipulating that a slave be emancipated upon his owner’s death. It is established that the Prophet, peace and blessings be upon him, sold a slave whose emancipation had been stipulated in this way to repay a debt. And Allah knows best.

He was asked:

Concerning someone who designated an endowment to provide candles or oil for the grave of the Messenger of Allah, peace and blessings be upon him, to take effect after his own death. He then wished to change the endowment and dedicate it to the poor and needy in Cairo.

If that is not permissible, may he dedicate it to the poor residing in Medina—the city of the Messenger of Allah, peace and blessings be upon him—or not?