Mahabharata 13.10.49
शूद्रोऽहमभवं पूर्वं तापसो भृशसंयुतःऋषिरुग्रतपास्त्वं च तदाभूर्द्विजसत्तम
śūdro'hamabhavaṃ pūrvaṃ tāpaso bhṛśasaṃyutaḥṛṣirugratapāstvaṃ ca tadābhūrdvijasattama
Our plain-language meaning of this verse is waiting for scholar review.
Open in the book