Sayyiduna Jabir bin Abdullah (may Allah be pleased with him) said that the Messenger of Allah (peace and blessings be upon him) ruled concerning the lifelong grant ('umra): "When a man gifts something to another man and his heirs, and makes the exception: 'If anything happens to your heirs, it will come back to me and to my heirs,' it belongs to the one to whom it was given and to his heirs."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الهبات / 11967