‘Tis rare, when riches cannot taint the mind.

[Ardua res haec est opibus non tradere mores.]

Marcus Valerius Martial
Martial (AD c.39-c.103) Spanish Roman poet, satirist, epigrammatist [Marcus Valerius Martialis]
Epigrams [Epigrammata], Book 11, epigram 5 (11.5.3) (AD 96) [tr. Killigrew (1695)]
    (Source)

(Source (Latin)). Alternate translations:

Wealth to withstand, how arduous is the skill!
[tr. Elphinston (1782), Appendix to Book 1, ep. 12]

It is an arduous task to preserve morality from the corruption of riches.
[tr. Bohn's Classical (1859)]

'Tis a hard task not to surrender morality for riches.
[ed. Harbottle (1897)]

'Tis a hard task this, not to sacrifice manners to wealth.
[tr. Ker (1919)]

Riches sap morals.
[tr. Francis & Tatum (1924)]

It is a hard thing not to sacrifice morals to wealth.
[tr. Shackleton Bailey (1993)]

It is a hard business, not to compromise morals for riches.
[tr. Nisbet (2015)]