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.

It is narrated from Hasan (may Allah have mercy on him): If a man makes a will for someone, and the legatee (the one for whom the will is made) dies before the executor, Hasan (may Allah have mercy on him) said: Such a will shall be valid for the heirs of the legatee (i.e., the one for whom the will was made).

Abu Ishaq al-Sabi'i said: It was narrated to me that Sayyiduna Ali (may Allah be pleased with him) considered such a bequest to be permissible. (That is), according to the statement of Hasan (may Allah have mercy on him), he also said this.