Is it permissible to make a will entrusting someone with something, such as Hajj, before undergoing a dangerous surgical operation?

A will (wasiyyah (definition)) is of two types: obligatory (wajibah) and recommended (mustahabbah).

The obligatory will is for clarifying a person's rights and obligations, such as debts and trusts, in order to preserve their wealth and clear their conscience. This is based on the Prophet's (peace be upon him) saying: "It is not right for a Muslim who has something to bequeath to spend two nights without having his will written down with him."

As for the recommended will, it is to donate a third or less of one's wealth, for someone who leaves behind a large estate and whose heirs are not in need of it, to be used for good deeds. This is based on his (peace be upon him) saying: "Indeed, Allah, the Almighty and Majestic, has given you, at the time of your death, a third of your wealth as an increase in your deeds," and the hadith (definition) of Sa'd ibn Abi Waqqas, which states: "A third, and a third is much. It is better for you to leave your heirs wealthy than to leave them dependent, begging from people."

Hajj must be performed on behalf of someone who died without performing the obligatory Hajj, from their wealth, whether they made a will or not. However, for someone who performed the obligatory Hajj, Hajj is not performed on their behalf unless they specifically willed it, and it does not exceed one-third of the estate.

Therefore, it is advisable to write a will, as death comes suddenly.