“Art is long, life is short.”

Die Kunst ist lang, das Leben kurz, das Urteil schwierig, die Gelegenheit flüchtig.
Bk. VII, Ch. 9
Cf. Hippocrates, Ars longa vita brevis, Aphorisms 1:1
Wilhelm Meister's Lehrjahre (Apprenticeship) (1786–1830)

Part of the secret "call and response" codewords by which members of the long-lived Howard Families can identify others:
: Life is short.
But the years are long.
Not while the evil days come not.
Methuselah's Children (1958)

The Man in the High Castle (1962)

Source: Lady Midnight

Apparently an invention by Maurice Sachs; see discussion in Quotes about Proust.
Misattributed

UFC 178 post-event press conference https://www.youtube.com/watch?v=zAAC34JzxS0 (September 2014), Ultimate Fighting Championship, Zuffa, LLC
2010s, 2014

Source: Henry V

Maxim 124
Sentences, The Moral Sayings of Publius Syrus, a Roman Slave