Natyashastra
खटकाख्ये यदा हस्ते तर्जनी सम्प्रसारिता । हस्तः सूचीमुखो नाम तदा ज्ञेयः प्रयोक्तृभिः ॥ ६५॥
When the index finger is extended in the Kaṭakāmukha hand, it is known as the Sūcīmukha hand gesture.
english translation
khaTakAkhye yadA haste tarjanI samprasAritA । hastaH sUcImukho nAma tadA jJeyaH prayoktRbhiH ॥ 65॥
hk transliteration by Sanscript