Rudra-prasava-varṇana
The Manifestation and Naming of Rudra / Nīlalohita
एकाकी चश्चरत्येष सूर्यो ऽसौ रुद्र उच्यते / सूर्यस्य यत्प्रकाशेन वीक्षन्ते चक्षुषा प्रजाः
ekākī caścaratyeṣa sūryo 'sau rudra ucyate / sūryasya yatprakāśena vīkṣante cakṣuṣā prajāḥ
This Sun moves on alone; therefore it is called Rudra. By the Sun’s radiance, beings behold with their eyes.