Kalagnirudra Upanishad

It is attached to the Krishna Yajurveda. It is one of 14 Shaiva Upanishads. The Upanishad is a discourse by Kalagni Rudra (Shiva) to sage Sanatkumara on the Tripundra, the Shaiva sectarian tilaka consisting of three horizontal lines of sacred ash on the forehead. The allegorical significance of the "three ash lines", is that the tradition sees them as streaks of three Vedic fires, three audible syllables of AUM, three Guṇas, three worlds, three Atmans, three Vedas and three aspects of Shiva. The text extols the Tripundra and tells about the procedure for applying Vibhuti (sacred ash) as Tripundra on various parts of the body with the associated mantras and rites.