મોઢે કડવું કહે, વાંસે કાંઈ બોલે નહીં;

mōḍhē kaḍavuṁ kahē, vāṁsē kāṁī bōlē nahīṁ;

Literally: Speaks harshly to the face, says nothing behind the back.
What it means: Genuine friends express their criticism directly without slandering someone in their absence.

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.