Mahabharata 6.40.41

ब्राह्मणक्षत्रियविशां शूद्राणां च परंतपकर्माणि प्रविभक्तानि स्वभावप्रभवैर्गुणैः

brāhmaṇakṣatriyaviśāṃ śūdrāṇāṃ ca paraṃtapakarmāṇi pravibhaktāni svabhāvaprabhavairguṇaiḥ

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