Impermissibility of a will for an heir or for more than one third of the inheritance if it is established in courts when it is not written

Q: I would like to inform Your Eminence that my brother Adul-Rahman ibn Abdul `Aziz fell ill and was taken to hospital in Riyadh. While at hospital, he asked Brother Sulayman ibn Ibrahim ibn Wayil, who is known for his trustworthiness, to allocate one third of his wealth to the construction of a Masjid (mosque) and to give his brother Fahd a hundred thousand riyals of his wealth and other seven thousand riyals for his wife. He left hospital after he had recovered from his illness. Four months later, he was murdered. He left behind a mother, a wife, two paternal half-brothers, one maternal half brother and one paternal half-sister. Kindly enlighten us regarding the validity of his bequest and proper distribution of his inheritance. May Allah reward you best!

A: First: It is not permissible for a person to bequeath more than one-third of his wealth. No bequest must be made to an heir unless the pubescent heirs are content to deduct a portion of their shares for this purpose. This is based on the Hadith in which the Prophet (peace be upon him) is reported to have said: Allah has appointed for everyone who has a right what is due to him, and no bequest must be made to an heir. Narrated by Ahmad, Abu Dawud, Al-Tirmidhy, Ibn Majah, and Al-Daraqutny. The following addition is found in the narration of Imam Ahmad: Unless the heirs so wished. (Part No. 16; Page No. 318)  Second: The bequest has to be documented at the Shari`ah courts of law. Third: After paying off the deceased's debts and executing his will, the leftover of his wealth has to be divided among the heirs into sixty equal shares: the mother shall inherit one-sixth of the wealth (ten shares out of the sixty), the wife shall inherit one-fourth of the wealth (fifteen shares out of the sixty), his maternal half brother shall inherit one-sixth (ten shares out of the sixty) and the remaining twenty five shares shall be distributed among his two half-brothers and his half-sister, ten given to the male and five to the female. May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.