Ibn Abi Dhi'b narrated from Ibn Shihab, from Abu Salamah, from Jabir, that the Messenger of Allah ruled -concerning a person who has been given a lifelong gift ('Umra)- that it belongs to him and to his descendants:
It is undoubtedly his, and it is not permissible for the giver to stipulate any conditions or exceptions. Abu Salamah said: Because he gave it as a gift and thus, it is subject to the same ruling as the estate, and the condition (that it will revert to the giver on the death of recipient) has become invalid.