Bhagavatapurana 3.6.29

3.6.29

tārtīyena svabhāvena bhagavan-nābhim āśritāḥ /
ubhayor antaraṃ vyoma ye rudra-pārṣadāṃ gaṇāḥ //

29. By virtue of the third Guna (Tamas), the groups of Rudra's servants (attendants) have occupied the Almighty Lord's navel, viz., the sky which is midway between the aforesaid two regions (of the gods and of men).