DORINE: Those who have the greatest cause for guilt and shame
Are quickest to besmirch a neighbor’s name.

[Ceux de qui la conduite offre le plus à rire
Sont toujours sur autrui les premiers à médire.]

Molière (1622-1673) French playwright, actor [stage name for Jean-Baptiste Poquelin]

Tartuffe, Act 1, sc. 1 (1664) [tr. Wilbur (1963)]
    (Source)

Alt. trans.:

• "They whose own conduct is the most ridiculous are always the first to slander others." [tr. Van Laun (1876)]
• "Since they are always talked about, / They're sniffing other scandal out." [tr. Bolt (2002)]
• "Those whose conduct gives room for talk / Are always the first to attack their neighbors." [Bartlett's]

Original French.