Natyashastra
पञ्चषट्सप्त तानि स्युः शीर्षकं च परान्तके । प्रकर्यामथ चत्वारि स्युस्त्रीण्यर्धाधिकानि च ॥ १९१॥
Those [songs] number five, six, or seven, and there is a Śīrṣaka at the end. In the Prakarī, there are four [Vastus] and three and a half [Vastus] as well.
english translation
paJcaSaTsapta tAni syuH zIrSakaM ca parAntake । prakaryAmatha catvAri syustrINyardhAdhikAni ca ॥ 191॥
hk transliteration by Sanscript