al-Husain bin Dhakwan al-Mua'lam الحسين بن ذكوان المعلم المكتب · The Book of 'Umra

"Any man who gives a lifelong gift to another man, it belongs to him (the recipient) and his descendants. He said: 'I have given it to you and to your descendants so long as any of you are still alive.' So it belongs to the one to whom it was given, and it cannot revert to the first owner, since he has given it as a gift, and as such, it becomes subject to the same ruling as the estate."