Mahabharata 13.131.11

स द्विजो वैश्यतामेति वैश्यो वा शूद्रतामियात्स्वधर्मात्प्रच्युतो विप्रस्ततः शूद्रत्वमाप्नुते

sa dvijo vaiśyatāmeti vaiśyo vā śūdratāmiyātsvadharmātpracyuto viprastataḥ śūdratvamāpnute

Our plain-language meaning of this verse is waiting for scholar review.