In Japanese it's 形ある物いつかは壊れる katachi aru mono (things that have shape) itsuka (eventually, some day) wa (emphasizing the inevitability of itsuka, I think) kowareru (break).
There's a lot of entries for that and even more if you do variants- itsuka alone or kanarazu (inevitably). Very few people cite sources. 'An old saying' 'a Buddhist saying' 'something they said in olden days- pretty smart, those olden days guys' and even 'some westerner in history.' It's a common saying, whatever, even if the exact source is obscure.
I'm pretty sure it's Buddhist and possibly riffing off the Noble Truth that all is impermanent. Alas, in Japanese the Noble Truth gets expressed by quite different kanji- 諸行無常 shogyou mujou- which a reader of modern Japanese might be tempted to take as All goings, nothing regular: the plight of mvrdrk's chronically business-tripping World Traveller.
However in amongst the wps was a link to a jataka, tales of the Buddha's life, in which he consoled a grieving father with something close to katachi aru mono kowareru. Couldn't find an English translation, did find a paraphrase: "all conditioned realities are subject to dissolution." Er, yes. I guess that's what it's saying. The Japanese just didn't want to say that all things melt.
It's that kowareru. Rather as mujo's jo has two meanings (normal, regular as well as- by extension? or originally? continual, unending) so with kowareru. It usually has the meaning of break into pieces or break down, but religiously the meaning has to be the more diffuse dissolve, come apart- thaw and resolve itself into a dew, even. There just seems no way to say it in English without likening the whole physical world to alarm clocks. "All that has form inevitably will come apart."
The problem, if you consider it a problem, exists in Japanese too. A good 90% of the webpages quoted 'katachi aru mono itsuka wa kowareru' before advising their readers to back-up their hard drives. Because everything that has a body will break. Nod nod, common sense that.
(No, of course I didn't write this to explicate a troublesome line in the Gaiden. I did it so I could tell you about a Japanese witticism. Because I can't resist a pun. Like the car in The Phantom Tollbooth that you have to be silent if you want it to move, because it goes without saying.)