Natyashastra
पूर्वेषामेव गीतानां यान्यङ्गानि स्मृतान्यथ । तेषां वृत्तविधौ कार्यमेककं विवधोऽथवा ॥ १६॥
The limbs earlier described for the songs should be applied according to rule as Vṛtta, Vivadha, or Ekaka.
english translation
pUrveSAmeva gItAnAM yAnyaGgAni smRtAnyatha । teSAM vRttavidhau kAryamekakaM vivadho'thavA ॥ 16॥
hk transliteration by Sanscript