From Sahih Muslim (Hadith 4190):
Jabir b. 'Abdullah al-Ansari (Allah be pleased with him) said:Allah's Messenger (ﷺ) 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
Reference: Muslim 4190