Messenger of Allah ﷺ said: Whoever a person conferred Umra (life grant) upon a person and he says: I confer upon you this and upon your descendants and anyone who survives you, and that becomes his possession and that of his posterity. It would become (a permanent possession) of those who were conferred upon this gift, and it would not return to its owner (donor), for he gave that as a gift in which accrued the right of inheritance. (Using translation from Muslim 1625c)
أَنَّ رَسُولَ اللهِ ﷺ قَالَ «أَيُّمَا رَجُلٍ أَعْمَرَ رَجُلًا عُمْرَى لَهُ وَلِعَقِبِهِ» قَالَ «قَدْ أَعْطَيْتُكَهَا وَعَقِبَكَ مَا بَقِيَ مِنْكُمْ أَحَدٌ فَإِنَّهَا لِمَنْ أُعْطِيَهَا وَإِنَّهَا لَا تَرْجِعُ إِلَى صَاحِبِهَا؛ مِنْ أَجْلِ أَنَّهُ أَعْطَى عَطَاءً وَقَعَتْ فِيهِ الْمَوَارِيثُ»