Vishnupurana 1.14.19

1.14.19

daśavarṣasahasrāṇi nyastacittā jagatpatau /
nārāyaṇe muniśreṣṭha sarvalokaparāyaṇe //

Thus instructed by their father, the ten Prachetasas plunged into the depths of the ocean, and with minds wholly devoted to Náráyańa, the sovereign of the universe, who is beyond all worlds, were engrossed by religious austerity for ten thousand years: remaining there, they with fixed thoughts praised Hari, who, when propitiated, confers on those who praise him all that they desire.