ભલો ભલાઈ ના તજે, દુષ્ટ ન ચુકે દાવ;

bhalō bhalāī nā tajē, duṣṭa na cukē dāva;

Literally: A good person does not abandon goodness, and a wicked person does not miss an opportunity to strike.
What it means: People act according to their inherent nature, with the virtuous remaining kind and the malicious remaining deceitful regardless of circumstances.

Also said as

ગુજરાતી કહેવતસંગ્રહ (Gujarati Kahevat Sangrah) (1923) · read from the scan by machine — the Gujarati itself is unchecked · English is machine-made and nobody has checked it yet

Heard it differently, or know we've got the sense wrong? Tell us — that is exactly the kind of correction this needs.