This, too, shall pass away.
I myself got this from a Larry Niven short story, “Not Long Before the End,” one of the science fiction author’s few (perhaps his only) forays into fantasy. It was part of an anthology, Treasures of Fantasy, put together by Margaret Weiss and Tracy Hickman.
It is, however, an old saying even in this world. There’s at least one poem that uses it, but it certainly didn’t invent it and is not especially great in my opinion, so never mind that. This site says that it’s actually an old Persian proverb, transcribed into Hebrew, which makes sense. In any case, it’s a hell of a point, though one I don’t much care to think about much, since it’s pretty depressing.