Sayyiduna Jabir bin Abdullah (may Allah be pleased with him) said: The lifelong grant ('umra) that the Messenger of Allah (peace and blessings be upon him) permitted is that he says: "It is yours and your heirs'." But if he says: "It is yours as long as you live," then it returns to its original owner.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الهبات / 11964