Natyashastra
बहिर्वा वर्धमाने वा कनिष्ठां न हि दक्षिणे । द्विगुणक्षीर(गुणाक्षर)संयोगादन्यमार्गनियोजनात् ॥ ८१॥
Whether outside the Vardhamāna or within it, the short (bāla) Tāla is never used in the Dakṣiṇa Mārga. This is because, by doubling the syllables (or Kalās) and applying other Mārgas, the Layāntara (tarita) is naturally established.
english translation
bahirvA vardhamAne vA kaniSThAM na hi dakSiNe । dviguNakSIra(guNAkSara)saMyogAdanyamArganiyojanAt ॥ 81॥
hk transliteration by Sanscript