દર દર મૂષક ન હોય, ક્યાંક નમેરા નાગ પણ હોય.

dara dara mūṣaka na hōya, kyāṁka namērā nāga paṇa hōya.

Literally: Every hole does not hold a mouse; in some there may be a ruthless cobra.
What it means: Caution is necessary because not every situation or person is harmless, and hidden danger may lurk.

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.