દહાડે ડોળાં ચારે, રાતે હીરા પારખે.

dahāḍē ḍōḷāṁ cārē, rātē hīrā pārakhē.

Literally: By day he grazes cattle, by night he evaluates diamonds.
What it means: Applied to a hypocrite or incompetent person who pretends to have high expertise outside his humble station.

Also said as

ગુજરાતી કહેવતસંગ્રહ (Gujarati Kahevat Sangrah) (1921) · 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.