Mudgalapurana 2.15.12

2.15.12

rasātalaṃ śailamayamadhastadvat sthitaṃ mahat |
vāsukipramukhairnāgairdaityairnānāvidhaistathā ||

Rasātala is rocky, situated beneath in the same way, being immense; / with serpents headed by Vāsuki and with various kinds of Daityas;