Wa `alaykum as-salamu wa rahmatullahi 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.
Brother, we appreciate your question, and we commend your keenness on getting yourself well-acquainted with the teachings of Islam. May Allah help us all keep firm on the right path.
It goes without saying that private ownership in Islam is absolutely respected, but the more an individual owns, the more responsibility he or she has toward society. In Islam, a Muslim has full control of his or her property to consume it, use it as a means of production, save it, or give it as charity.
However, the Islamic law puts some restrictions on the use of an individual’s property. For example, the individual cannot consume it wastefully or use it in the production or facilitation of unlawful goods or practices, like alcoholic beverages, and gambling.
In his response to your question, Prof. Dr. Monzer Kahf, a prominent economist and counselor, states:
The fact is: Every person has a full authority on what he or she owns as long as he or she is in normal mental capacity and not in a situation of a terminal illness that he or she will die within a year because this is the immediate implication of the right of ownership in Islam.
If the questioner [the lady] fulfills the above-mentioned conditions, regardless of her age, she can give to charity any amount and any property she owns. Her heirs (children) cannot even limit her power to do what she likes to do. There is an advice (only advice) from our most beloved Prophet (peace and blessings be upon him) that one is better to leave his heirs rich rather than to leave them poor. Leaving a half a million GBP to three sons and a girl, according to the current level of living in Britain, is leaving them rich, not poor.
I also suggest to her that if she decides to give such a large donation to an Islamic charity, she should make it a Waqf to the benefit of the charity rather than a donation and that she should make conditions in this Waqf so that the charity will have no right to sell these properties except for the purpose of buying another one that gives equal or better income and that the charity must take good care of the properties so that they give a continuous flow of net income while they stay permanent.
Almighty Allah knows best.