मनु स्मृति - नित्य धर्म - सूर्य

नेक्षेतोद्यंतमादित्यं नास्तंयंतं कदाचन |
नोपसृष्टं न वारिस्थं न मध्यं नभसो गतम् ||

- मनु स्मृति

One must not look at the sun directly just when it is rising, or setting, or at noon (directly above one's head), or its reflection in the water. Each of these have their own reasons not to be watched with naked eyes.

- Manu Smriti