Sahih Muslim Book 12, Hadith Number 3974.

Chapter : Al-‘Umra (Life grant).

Jabir b. ‘Abdullah al-Ansari (Allah be pleased with him) said: Allah’s Messenger (may peace be upon him) said: Whoever a person conferred Umra (life grant) upon a person and he says: I confer upon you this and upon your descendants and anyone who survives you, and that becomes his possession and that of his posterity. It would become (a permanent possession) of those who were conferred upon this gift, and it would not return to its owner (donor), for he gave that as a gift in which accrued the right of inheritance.