Natyashastra
चतुष्कलस्तु कर्तव्यो मद्रके तु चतुष्कले । त्रिवस्तु त्रिप्रमाणं च अस्रतालसमुद्भवम् ॥ २३४॥
In the Madraka of four Kalas, there should be three Vastus of three different measures, all arising from the Tryasra Tala.
english translation
catuSkalastu kartavyo madrake tu catuSkale । trivastu tripramANaM ca asratAlasamudbhavam ॥ 234॥
hk transliteration by Sanscript