કોયલની દલાલીમાં હાથ કાળા.

kōyalanī dalālīmāṁ hātha kāḷā.

Literally: Hands are black in the brokerage of the cuckoo.
What it means: Involvement in shady or dishonest dealings will inevitably stain one's reputation.

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.