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.
Srimad Bhagavata Purana
श्रीमद्भागवतमहापुराणम्
मूल श्लोकः
यदा मघाभ्यो यास्यन्ति पूर्वाषाढां महर्षयः । तदा नन्दात्प्रभृत्येष कलिर्वृद्धिं गमिष्यति
yadā maghābhyo yāsyanti pūrvāṣāḍhāṃ maharṣayaḥ | tadā nandātprabhṛtyeṣa kalirvṛddhiṃ gamiṣyati
SB 12.2.32