Vijnana Bhairava Tantra
कूपादिके महागर्ते स्थित्वोपरि निरीक्षणात् । अविकल्पमतेः सम्यक्सद्यश्चित्तलयः स्फुटम् ॥ ११५ ॥
Standing above a deep hole or well and looking steadily downward (into the abyss), the mind becomes entirely free of vikalpas and dissolution immediately manifests.
english translation
kUpAdike mahAgarte sthitvopari nirIkSaNAt । avikalpamateH samyaksadyazcittalayaH sphuTam ॥ 115 ॥
hk transliteration by Sanscript