Wa `alaykum As-Salamu waRahmatullahi wa Barakatuh.
In the Name of Allah, Most Gracious, Most Merciful.
All praise and thanks are due to Allah, and peace and blessings be upon His Messenger.
In this fatwa:
It is not permissible for you to sell or give away your right of inheriting the estate of your brother. However, after he passes away, it will be permissible. This is because it no longer remains a right as such, rather you own a proportionate share in his estate, which you can sell or give away to whomsoever you like.
In his answer to your question, Mufti Muhammad Ibn Adam Al-Kawthari, Director and researcher at the Institute of Islamic Jurisprudence (Darul Iftaa, www.daruliftaa.com), Member of the Al-Qalam Shari`ah Scholars Panel, and advisor on Islamic Banking, states;
Selling One’s Right of Inheritance
It is forbidden and invalid to sell, or even gift, one’s right of inheriting an estate to another person.
Abdullah ibn Umar (may Allah be pleased with him) relates that the Prophet (peace be upon him) forbade selling and giving away the right to inherit [the estate of] a slave (al-wala’). (Al-Bukhari and Muslim)
The term al-wala’ used in this hadith refers to the right of inheriting the estate of a slave. When a slave who was granted emancipation died, the one who set him free was entitled to inherit his estate when no other eligible heirs were present.
The Arabs would trade this right or give it away to others, hence the Messenger of Allah forbade it emphatically.
The renowned hadith scholars such as Imam Nawawi, Imam Al-`Ayni and others explain that: the ‘right to inherit’ is from those rights that have been explicitly granted by the Shariah. It is similar to the right of lineage, i.e. a person has a right to attribute himself to his father.
Such rights are not transferable from one person to another by way of sale, gift or any other method. There is, more or less, a consensus on this position. (An-Nawawi, Al-Minhaj sharh Sahih Muslim p: 1155, Al-`Ayni, Umdat al-Qari sharh Sahih al-Bukhari 9/335; and Usmani, Takmilat Fath al-Mulhim sharh Sahih Muslim 4/192)
The right to inherit is a permanent right
As such, the right to inherit (haq al-irth), whether the estate of a slave that one freed – as mentioned in the aforementioned hadith – or the estate of a family member, is a permanent right granted by the Shariah.
Thus, it is not permissible to sell, transfer or give away this right to another person, such that he is entitled to inherit the estate instead of the original heir. (Buhuth fi Qadaya fiqhiyya Mu’asarah, p. 84)
Moreover, in the case of selling one’s inheritance right, there is an element of chancing or uncertainty (gharar) which in itself is impermissible. The buyer pays the price to the seller in return for the right to inherit, but there is no guarantee that he will inherit anything, since it is possible that he dies before the person whose estate he is scheduled to inherit. Even if he lives longer and does inherit, there is no certainty of how much he will inherit, whilst the price he pays to acquire this right is certain. Islam rejects all contracts where one party pays the price in certainty, but the return is uncertain.
In summary, it is not permissible for you to sell or give away your right of inheriting the estate of your brother. However, after he passes away, it will be permitted, because it no longer remains a right as such, rather you own a proportionate share in his estate, which you can sell or give away to whomsoever you like.
Almighty Allah knows best.