Srimad-Bhagavatam: Canto 3 - Chapter 1 - Verse 15

Sanskrit:

सोऽशयिष्टाब्धिसलिले आण्डकोशो निरात्मक: ।साग्रं वै वर्षसाहस्रमन्ववात्सीत्तमीश्वर: ॥ १५ ॥

ITRANS:

so ’śayiṣṭābdhi-salileāṇḍakośo nirātmakaḥsāgraṁ vai varṣa-sāhasramanvavātsīt tam īśvaraḥ

Translation:

For over one thousand years the shiny egg lay on the waters of the Causal Ocean in the lifeless state. Then the Lord entered it as Garbhodakaśāyī Viṣṇu.

Purport:

From this verse it appears that all the universes are floating in the Causal Ocean.