‘Tis not, believe me, a wise man’s part to say, “I will live.” Tomorrow’s life is too late: live today.

[Non est, crede mihi, sapientis dicere “Vivam”:
Sera nimis vita est crastina: vive hodie.]

Martial (AD c.39-c.103) Spanish Roman poet, satirist, epigrammatist [Marcus Valerius Martialis]

Epigrams [Epigrammata], Book 1, epigram 15 (1.15.11-12) (AD 85-86) [tr. Bohn’s (1859)]
    (Source)

A sentiment echoed in 5.58. (Source (Latin)). Alternate translations:

Trust me, it is not wise to say,
I'll live; 'twill be too late tomorrow,
Live if thou'rt wise today.
[tr. Oldmixon (1728)]

"I'll live tomorrow," will a wise man say?
Tomorrow is too late, then live today.
[tr. Hay (1755), quoted in Bohn's, but not in Hay's own book]

Tomorrow I shall live, the fool will say. [...]
Wouldst thou be sure of living? Live today.
[tr. Elphinston (1782), Book 2, ep. 45]

No wisdom 'tis to say "I'll soon begin to live."
'Tis late to live tomorrow; live today.
[ed. Harbottle (1897)]

It sorts not, believe me, with wisdom to say "I shall live."
Too late is tomorrow's life; live thou today.
[tr. Ker (1919)]

"I'll live tomorrow," no wise man will say;
Tomorrow is too late. Then live today.
[tr. Francis & Tatum (1924), #10]

To say, "I mean to live," is folly's place:
Tomorrow's life comes late; live, then, today.
[tr. Duff (1929)]

It's not a wise man's part to say
"I'll live," Tomorrow's life is much to late.
Live! Today.
[tr. Bovie (1970)]

Believe me, the wise man does not say "1 shall live." Tomorrow's life is too late. Live today.
[tr. Shackleton Bailey (1993)]

No sage will e'er "I'll live tomorrow" say:
Tomorrow is too late: live thou today.
[tr. WSB]