All perfect praise be to Allah, The Lord of the worlds. I testify that there is none worthy of worship except Allah and that Muhammad is His slave and Messenger.
The will of the father to divide his estate after his death in a manner that is contrary to the laws of inheritance in the Sharia is null and void. However, if any of the heirs is a mature rational adult and agrees to take less than his legitimate share in the inheritance, to conform to the wish of his father, then there is nothing wrong in it.
As for the heirs who are young or are adult but not rational, then their consent is not taken into account and their legitimate share in the inheritance must be kept for them.
In addition to this, if an heir keeps silent regarding not taking his full legitimate share, then this is not considered a sign of consent; perhaps he kept silent because of believing that the will of his father must be implemented and that he has no right to object, but had he known of his right to object and that it is not obligatory to implement his father’s will, he maybe would not have kept silent and would have asked for his full right.
The scholars stated that in principle silence is not a permission; this is for the rule: “No speech is attributed to one who has remained silent”
Az-Zarkashi said, “Silence by itself is considered a declaration (utterance) in regard to someone who is infallible, but regarding a person who is not infallible, then in principle his silence is not considered a declaration unless there are indications that prove his consent; in which case his silence is interpreted to mean a declaration (utterance).”
The Fiqh Encyclopedia reads, “There is no doubt that passive silence is not a sign of consent or lack of consent; hence, the Fiqh ruling stipulates that, ‘No speech is attributed to one who has remained silent. But silence in case of need is a statement; this is so if it is accompanied by evidence and circumstances which make it indicate consent.’”
Allah knows best.