What is the ruling regarding a father's bequest of one-third (of his estate) to his grandson, given that he has six daughters, two sons, and two unmarried daughters, one 54 years old and the other 50 years old?

This will is valid and enforceable because it is not for an heir and does not exceed one-third [of the estate]. The Messenger of Allah, peace be upon him, said: "Indeed, Allah has bestowed upon you, at the time of your death, one-third of your wealth as an increase for you in your deeds." This will is valid for grandchildren even if there is a direct son.