Matsyapurana 4.37

4.37

divyamāpa tataḥ sthānam acalaṃ brahmaṇo varāt
tameva purataḥ kṛtvā dhruvaṃ saptarṣayaḥ sthitāḥ //

“In the bygone ages, Dhruva practised severe penances for a period of three thousand years and obtained from Brahmâ an abode in the eternal celestial regions. The Saptariṣîs, acknowledging him as their chief clustered themselves round him.”—36-37.