The Umra for which Messenger of Allah ﷺ gave sanction that a person way say: This (property) is for you and for your descendants. And when he said: That is for you as long as you live, then it will return to its owner (after the death of the donee). Ma'mar said: Zuhri used to give religious verdict according to this.
إِنَّمَا الْعُمْرَى الَّتِي أَجَازَ رَسُولُ اللَّهِ ﷺ أَنْ يَقُولَ هِيَ لَكَ وَلِعَقِبِكَ فَأَمَّا إِذَا قَالَ هِيَ لَكَ مَا عِشْتَ فَإِنَّهَا تَرْجِعُ إِلَى صَاحِبِهَا قَالَ مَعْمَرٌ وَكَانَ الزُّهْرِيُّ يُفْتِي بِهِ