I'm thinking it's a saying. Here are some of the attributions I saw for it:
We don't inherit the earth from our ancestors, we borrow it from our children.
~ American Indian philosophy
David Brower (environmentalist) [I doubt that he originated it]
Pennsylvania Dutch saying
Nous n'heritons pas cette terre de nos ancetres, mais nous l'empruntons de nos enfants.
We don't inherit the earth from our ancestors, rather we borrow it from our children.