Vijnana Bhairava Tantra
सम्कोचं कर्णयोः कृत्वा ह्यधोद्वारे तथैव च । अनच्कमहलं ध्यायन्विशेद्ब्रह्म सनातनम् ॥ ११४ ॥
Contracting (or closing) the openings of the ears and also the lower opening (reproductive/excretory organs) in the same way, and then meditating on the palace of the anahad (unstruck) sound within, one enters die eternal Brahma.
english translation