Sayyiduna Jabir bin Abdullah (may Allah be pleased with him) said: The Messenger of Allah (peace and blessings be upon him) ruled concerning someone given a lifelong grant ('umra) for himself and his heirs that "it is his outright; no condition is permissible for the giver in it, nor any exception." Abu Salamah (may Allah have mercy on him) said: "Because he has given a gift in which inheritance has come into effect, and the inheritance has cut off his condition."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الهبات / 11966