Sahih Muslim Book 012, Hadith Number 3976.
Chapter : Al-'Umra (Life grant).
Jabir b. 'Abdullah (Allah be pleased with him) reported that Allah's Messenger (may peace be upon him) commanded that whoever is conferred upon a life grant along with his descendants is entitled to make use of the property conferred so long as he lives and his successors (also enjoy this privilege). That (property) becomes the their defect belonging. The donor cannot (after declaring Umra) lay down any condition or make any exception. Abu Salama said: For he conferred a grant and as such it becomes heritage and the right of inheritance abrogated his condition.