All other knowledge is harmful to him who has not the knowledge of goodness.

[Toute autre science, est dommageable à celuy qui n’a la science de la bonté.]

Michel de Montaigne (1533-1592) French essayist

Essays, Book 1, ch. 24 “Of Pedantry [Du pedantisme]” (c. 1572-78) (1.24) (1595) [tr. Ives (1925), ch. 25]
    (Source)

While the original essay dates back to 1572-1578 and the first edition, this passage was added 1588–1592 for the 1595 edition.

(Source (French)). Alternate translations:

Each other science is prejudciall unto him that hath not the science of goodnesse.
[tr. Florio (1603)]

All other knowledge is detrimental to him who has not the science of becoming a good man.
[tr. Cotton (1686); Friswell (1868)]

All other knowledge is hurtful to him who has not the science of goodness.
[tr. Cotton/Hazlitt (1877)]

All other learning is hurtful to him who has not the knowledge of honesty and goodness.
[tr. Rector (1899)]

Any other knowledge is harmful to a man who has not the knowledge of goodness.
[tr. Frame (1943), ch. 25]

All other knowledge is harmful in a man who has no knowledge of what is good.
[tr. Screech (1987), ch. 25]