Answered by Mufti Mohammed Tosir Miah
Question:
Asalaamu alaikum wa Rahmatualli wa barakatu. My house in which I am currently living in is worth approx. £70,000. After my death this will be distributing amongst my sons and daughters. Does the sharia allow me to allocate a portion of wealth from the sale of the house for myself after my death to be used as a Sadaqa Jariya so that I may be rewarded in the hereafter? If so how much does the sharia instruct that I could leave for this purpose?
Answer:
Literally wasiyyah means an order to do something, either in the lifetime of the maker of the wasiyyah or after his death. But in commonly accepted usage, it refers to what must be done after death. It can be translated as the Will or bequest.
According to the consensus of the Muslim Ummah it is not obligatory on the dying person to necessarily make a Will in favour of relatives who have no defined shares in the inheritance. The obligatory character of a wasiyyah in their favour is abrogated. The making of a Will in favour of such relatives is only a desired (mustuhab) act.
Furthermore, it is not permissible to make a Will for an inheritor.
It is narrated by Saaiduna Ibn Abbas 
that the Prophet of Allah 
has said, “Allah has Himself given everyone, who has a right, his right. So there is no will for any inheritor.” (Sunan Tirmizi)
The reason being is that Allah (SWA) has Himself fixed the shares of the inheritors; therefore the executor need not make a Will. (Maariful Quran p.450-p.452 v.1)
With regards to your question, it will be permissible for you to make a bequest of up to one third of your property after the funeral expenses and payments of debts, for a good noble cause so that you may get perpetual reward in the Hereafter.
It is narrated by Saaiduna Abu Hurairah that the Prophet of Allah said, “When a man dies, his deeds come to an end except for three things: Sadaqah Jariyah (ceaseless charity); a knowledge which is beneficial, or a virtuous child who prays for him (for the deceased).” (Sahih Muslim)
Only Allah Knows Best
Mohammed Tosir Miah
Darul Ifta Birmingham