Natyashastra
यथाक्षरेषु भूयिष्ठं गीतेष्वासारितेषु च । विधिरेष समुद्दिष्टो वर्णतालपदाश्रयः ॥ ११६॥
As the songs (Gītas) and Āsāritas consist mostly of syllables (akṣaras), this rule has been laid down— it is based upon the syllables (varṇa), the time-measure (tāla), and the words (pada).
english translation
yathAkSareSu bhUyiSThaM gIteSvAsAriteSu ca । vidhireSa samuddiSTo varNatAlapadAzrayaH ॥ 116॥
hk transliteration by Sanscript