Does the Hadeeth “No will for an heir” mean that a will must not absolutely be made for the benefit of an heir, or that the will may involve bequeathing one third of the wealth, and no more?

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and Messenger.

The Hadeeth that you have mentioned is narrated by Imaam Ahmad in Al-Musnad and also by Abu Daawood, An-Nasaa'i, At-Tirmithi and Ibn Maajah . It is such a famous Hadeeth among scholars that it has become a known rule.

It is narrated on the authority of ‘Amr ibn Khaarijah that the Prophet, sallallaahu ‘alayhi wa sallam, delivered a Khutbah (sermon) while riding his she-camel, and ‘Amr heard him say, “Allaah has given everyone who is entitled his rights, so there shall be no will for an heir.” [At-Tirmithi: Hasan Saheeh]

According to ‘Awn Al-Ma‘bood and other references, this Hadeeth means that Allaah Almighty explained the share of each heir in the verse of inheritance. Before this verse was revealed, it was obligatory to make a will for the relatives, based on the verse of the will that was abrogated by the verse of inheritance, according to many Muslim scholars. The abrogated verse of will says (what means): {Prescribed for you when death approaches [any] one of you if he leaves wealth [is that he should make] a bequest for the parents and near relatives according to what is acceptable.}[Quran 2:180]

The will that is made for an heir is invalid according to many scholars, so as to protect the rights of other heirs. If the other heirs permit the bequest, then it is valid. The same logic applies if they permit giving more than one third of the wealth to a non-heir.

Some scholars argue that it is not permissible to make a will for an heir even if the rest of the heirs allow it, because the prevention of will is the right of Sharee‘ah.

The sound view that was adopted by the majority of scholars is that a will is not permissible to be made for an heir or to include more than one third of the wealth unless permitted by the heirs – only then does it become valid. This is provided that the permitting heirs are adults and in full possession of their mental faculties. In Al-Insaaf, the eminent Hanbali scholar Al-Mardaawi said:

It is not permissible for a person who has heirs to make a will of more than one third [of the wealth] to a non-heir or [a bequest] to an heir [of any extra amount than the due share], unless he has the permission of the [rest of the] heirs.

Allaah Knows best.