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.