Ramayana
लक्षणज्ञांश्च गान्धर्वान्नैगमांश्च विशेषतः । पादाक्षरसमासज्ञांश्छन्दःसु परिनिष्ठितान् ॥ 7-94-6 ॥
And especially those who knew the marks of music, the Gandharvas, and the men learned in scripture, those who understood feet, syllables, and compounds, and those thoroughly accomplished in metres.
english translation