Vijnana Bhairava Tantra
एवमेव दुर्निशायां कृष्णपक्षागमे चिरम् । तैमिरं भावयन् रूपं भैरवं रूपमेष्यति ॥ ८७ ॥
Like this, one should ever contemplate on the terrible darkness of night during the dark fortnight of the moon, if he desires to attain the form of bhairava.
english translation