Natyashastra
विधानोपगताश्चार्यो व्यायच्छन्ते परस्परम् । यस्मादङ्गसमायुक्तास्तस्माद्व्यायाम उच्यते ॥ २॥
As the Cārīs prescribed by rules and connected with ॥ different॥ limbs relate to (vyāyacchante from vyā-yam = stretch out to) one another, they constitute (lit. are called) a vyayāma (system).
english translation
vidhAnopagatAzcAryo vyAyacchante parasparam । yasmAdaGgasamAyuktAstasmAdvyAyAma ucyate ॥ 2॥
hk transliteration by Sanscript