મેસથી કાળું કલંક.

mēsathī kāḷuṁ kalaṁka.

Literally: A stain blacker than soot.
What it means: A disgrace or loss of reputation that is extremely deep and impossible to wash away.

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.