Natyashastra
एतानि तु बहिर्गीतान्यन्तर्यवनिकागतैः । प्रयोक्तृभिः प्रयोज्यानि तन्त्रीभाण्डकृतानि च ॥११॥
These external songs, brought in by the actors from beyond the stage, should be used by the performers and accompanied by instruments.
english translation
etAni tu bahirgItAnyantaryavanikAgataiH । prayoktRbhiH prayojyAni tantrIbhANDakRtAni ca ॥11॥
hk transliteration by Sanscript