Vijñāna Bhairava Tantra 1.62

1.62

अमूलं मूलनाडीनां वायुपूर्णां सुषुम्णिकाम् । द्वादशान्ते स्थितां ध्यात्वा अमूलं भैरवं व्रजेत् ॥६२॥

amūlaṃ mūlanāḍīnāṃ vāyupūrṇāṃ suṣumṇikām | dvādaśānte sthitāṃ dhyātvā amūlaṃ bhairavaṃ vrajet

anuṣṭubh

— rootless (the rootless source) ; — of the root-channels ; — filled with breath ; — the suṣumnā channel ; — abiding at the dvādaśānta ; — having meditated ; — one goes to the rootless Bhairava

Meditating on the Suṣumnā — the rootless root of the root-channels — filled with breath, abiding up to the dvādaśānta, one reaches the rootless Bhairava.