Trust in another’s goodness is no light testimony to one’s own.

[La fiance de la bonté d’autruy, est un non leger tesmoignage de la bonté propre]

Michel de Montaigne (1533–1592) French essayist

Essays, Book 1, ch. 14 (1.14), “The Taste of Good and Bad Things Depends Mostly on the Opinion We Have of Them [Que le goust des biens et des maux despend en bonne partie de l’opinion que nous en avons]” (1572) [tr. Screech (1987)]
    (Source)

Writing admirably of an elderly prelate who had turned over management of his household and wealth to a succession of trusted servants.

This essay was in the 1st ed. (1580), but was expanded substantially for subsequent editions. This passage first appeared in the 3rd edition (1595). It is in Book 1, number 40 in most older translations; some more recent ones (as noted) number it as 14.

(Source (French)). Other translations:

The confidence in others honestie, is no light testimonie of ones owne integritie [Confidence in others’ honesty is no light testimony of one’s own integrity].
[tr. Florio (1603)]

The confidence of another Mans vertue, is no light evidence of a Mans own.
[tr. Cotton (1686)]

The confidence in another man's virtue is no light evidence of a man's own.
[tr. Cotton/Hazlitt (1877)]

Confidence in another's goodness is no slight testimony of one's own goodness.
[tr. Ives (1925), 1.14]

Confidence in the goodness of others is no slight testimony to one's own goodness.
[tr. Frame (1943), 1.14]

Trust in the goodness of others truly testifies to the goodness in ourselves.
[tr. HyperEssays (2025)]