Sunan ad-Darimi

It is narrated from Mak'hool (may Allah have mercy on him): If a man makes a bequest to spend dinars in the way of Allah for someone, and the one for whom the bequest was made passes away before the testator, he said: Before it leaves the hands of the heirs of the testator, such a bequest is permissible for the heirs of the one for whom the bequest was made. He also said: It is the responsibility of the heirs of the deceased testator to execute this bequest in the way of Allah.