The Messenger of Allaah (peace and blessings of Allaah be upon him) said: “It is not permissible to bequeath something to an heir unless the other heirs agree.” Narrated by al-Daaraqutni; classed as hasan by al-Haafiz Ibn Hajar in Buloogh al-Maraam.
Ibn Qudaamah (may Allaah have mercy on him) said in al-Mughni (6/58): If (the deceased) left a bequest to an heir, and it is not approved of by the other heirs, then it is not valid, and there is no difference of opinion among the scholars on this point. Ibn al-Mundhir and Ibn ‘Abd al-Barr said: The scholars are unanimously agreed on this point and there are reports from the Messenger of Allaah (peace and blessings of Allaah be upon him) concerning that. Abu Umaamah narrated: I heard the Messenger of Allaah (peace and blessings of Allaah be upon him) say: “Allaah has given each person who has rights his rights, and there is no bequest for an heir.” Narrated by Abu Dawood, Ibn Majaah and al-Tirmidhi … If they allow it, it is permissible, according to the majority of scholars. End quote.
It says in Fataawa al-Lajnah al-Daa’imah (16/317): It is not permissible to bequeath more than one-third, and it is not valid to bequeath to an heir, unless the adult heirs give their consent with regard to their share, because the Prophet (peace and blessings of Allaah be upon him) said: “Allaah has given each person who has rights his rights, and there is no bequest for an heir.” Narrated by Ahmad, Abu Dawood, al-Tirmidhi and Ibn Majaah, and by al-Daaraqutni who added at the end: “unless the heirs agree.” End quote.
“These are the limits (set by) Allaah (or ordainments as regards laws of inheritance), and whosoever obeys Allaah and His Messenger (Muhammad صلى الله عليه وسلم) will be admitted to Gardens under which rivers flow (in Paradise), to abide therein, and that will be the great success.
1. And whosoever disobeys Allaah and His Messenger (Muhammad صلى الله عليه وسلم), and transgresses His limits, He will cast him into the Fire, to abide therein; and he shall have a disgraceful torment”
[al-Nisa’ 4:13, 14]
What the heirs must do is cancel this bequest and divide the inheritance as enjoined by Allaah; it is not permissible for them to transgress against the rights of the females in accordance with this bequest.
If they do so, their sin will be even greater and even worse, because they are the ones who usurped the right from those who were entitled to it. We ask Allaah to guide them.
And Allaah knows best.