Iron rusts from disuse, stagnant water loses its purity and in cold weather becomes frozen, even so does inaction sap the vigor of the mind.

Leonardo da Vinci (1452–1519) Italian artist, engineer, scientist, polymath

The Notebooks of Leonardo da Vinci, Vol. 1, ch. 2 “Aphorisms” (1888) [ed/tr. McCurdy (1938 ed.)]
    (Source)

Source noted as Codice Atlantico 289 v. c.