We should be more ashamed to distrust our friends than to be deceived by them.
 
[Il est plus honteux de se défier de ses amis que d’en être trompé.]

François VI, duc de La Rochefoucauld (1613-1680) French epigrammatist, memoirist, noble

Réflexions ou sentences et maximes morales [Reflections; or Sentences and Moral Maxims], ¶84 (1665-1678) [tr. Heard (1917)]
    (Source)

First appeared in the second (1666) edition. Compare to Maxim 86, also from that edition: "Our distrust justifies the deception of others [Notre défiance justifie la tromperie d’autrui.]"

(Source (French)). Alternate translations:

It is much less for a Man's Honour to distrust his Friends, than to be deceived by them.
[tr. Stanhope (1694), ¶85]

It is more dishonourable to distrust a friend, than to be deceived by him.
[pub. Donaldson (1783), ¶171; ed. Lepoittevin-Lacroix (1797), ¶81; ed. Carvill (1835), ¶151]

It is more disgraceful to distrust; one's friends than to be deceived by them.
[ed. Gowens (1851), ¶87]

It is more disgraceful to distrust than to be deceived by our friends.
[tr. Bund/Friswell (1871), ¶84]

It is more disgraceful to mistrust one's friends than to be the victim of their treachery.
[tr. Stevens (1939), ¶84]

It is more shameful to distrust one's friends than to be deceived by them.
[tr. FitzGibbon (1957), ¶84; tr. Tancock (1959), ¶84]

It is more shameful to distrust our friends than to be deceived by them.
[tr. Kronenberger (1959), ¶84; tr. Whichello (2016), ¶84]