Sambhavi-mudra, the Great Seal of the Absolute

http://amritananda-natha-saraswati.blogspot.com/p/sambhavi-mudra-p-muller-ortega.html

antarlakṣya bahirdṛṣṭirnimeṣonmeṣavarjitā |
 eṣā sā śāmbhavī mudrā sarvatantreṣu gopitā | 

"Even though gazing outside, the eyes neither opening nor closing, one should direct one's attention within. This is the seal (mudra) of Bhairava, concealed as the best secret of all the Tantras."