Mahabharata 12.182.1

भरद्वाज उवाच · bharadvāja uvāca

ब्राह्मणः केन भवति क्षत्रियो वा द्विजोत्तमवैश्यः शूद्रश्च विप्रर्षे तद्ब्रूहि वदतां वर

brāhmaṇaḥ kena bhavati kṣatriyo vā dvijottamavaiśyaḥ śūdraśca viprarṣe tadbrūhi vadatāṃ vara

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