From Sahih Muslim (Hadith 4189):
Jaber b. 'Abdullah (Allah be pleased with them) reported Allah's Messenger (may peace be upan him) as saying:He who conferred a life grant upon a person, it becomes his possession and that of his successors, for he surrendered his right in that by his declaration. (This property) now belongs to one to whom this lifelong grant has been made, and to his successors. Yahya narrated in the beginning of his narration: Whatever man is given a life grant, then it belongs to him and his posterity
Reference: Muslim 4189