Vignana Bhairava Tantra - 128

Focus on the void

नित्ये निराश्रये शून्ये व्यापके कलनोज्झिते |
बाह्याकाशः मनः कृत्वा निराकारं समाविशेत् ||

Let the mind focus on the eternal, the independent void, spread everywhere, with no possibility of calculating its length, breath and height. In this space outside, place your mind and enter the spaceless void completely. - SS.