Garudapurana 1.50.45

1.50.45

ācāntaḥ punarācāmenmantreṇānena mantravit /
antaścarasi bhūteṣu guhāyāṃ viśvatomukhaḥ //

Having sipped water, the knower of mantras should sip water again with this mantra: / 'You move within beings, inside the cave of the heart, facing in all directions;