Srimad-Bhagavatam: Canto 12 - Chapter 1 - Verse 32
Sanskrit:
यदा मघाभ्यो यास्यन्ति पूर्वाषाढां महर्षय: ।तदा नन्दात् प्रभृत्येष कलिर्वृद्धिं गमिष्यति ॥ ३२ ॥
ITRANS:
yadā maghābhyo yāsyantipūrvāṣāḍhāṁ maharṣayaḥtadā nandāt prabhṛty eṣakalir vṛddhiṁ gamiṣyati
Translation:
When the great sages of the Saptarṣi constellation pass from Maghā to Pūrvāsāḍhā, Kali will have his full strength, beginning from King Nanda and his dynasty.