Mahabharata 12.49.4

उग्रं तपः समातिष्ठत्सहस्राक्षसमो भुविपुत्रं लभेयमजितं त्रिलोकेश्वरमित्युत

ugraṃ tapaḥ samātiṣṭhatsahasrākṣasamo bhuviputraṃ labheyamajitaṃ trilokeśvaramityuta

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