Natyashastra
नियमो या(यो) यतिः स्यात्तु गीतवाद्यसमाश्रयः । समपाणिश्च विज्ञेयो ह्यवपाणिस्तथैव च ॥ ३३४॥
The rule known as Yati (pause or rhythmic division) applies equally to song and instrumental music. It is recognized as of two kinds — Sama-pāṇi (equal or balanced beat) and Avapāṇi (uneven or descending beat).
english translation
niyamo yA(yo) yatiH syAttu gItavAdyasamAzrayaH । samapANizca vijJeyo hyavapANistathaiva ca ॥ 334॥
hk transliteration by Sanscript