Someone suffering from a fatal disease wishes to grant most of his inheritance to a certain group of his heirs, for he knows they are more in need compared to his other heirs. Is it permissible for him to grant huge amounts of his wealth to some heirs? Can he take an oral or written pledge from the other heirs to give up their shares?

The basic ruling, according to many scholars, is that a Muslim on his death bed cannot grant any of his wealth to anyone, for he is not legally competent at that time. In addition, it is not permissible for him to prefer some heirs to others.
Yet, it is permissible for him to ask the rest of the heirs to give up some of their inheritance to the poorer ones. If the heirs comply after his death, it will be good and they will also be acting dutifully towards him, but if they do not, there is no harm on them because giving this gift is not binding as long as it was not received as such. It is a gift related to someone’s death, and thus it is not binding, unless the rich heirs wish to do it. In which case, it will be better and preferable. Only Imam Malik declares it is binding and believes it is permissible for the poor heirs to sue the richer ones for them (the poor) to receive this gift. Allah knows best!