In his 1803 book Traité d’économie politique (Treatise on Political Economy), Say wrote (in the original French):

« C’est la production qui ouvre des débouchés aux produits »
(Translation: “It is production which opens outlets for products”)

This idea was later paraphrased and popularized in English as “Supply creates its own demand”, especially in 19th- and 20th-century economics textbooks.