Srimad-Bhagavatam: Canto 12 - Chapter 1 - Verse 13
Sanskrit:
तत एकोदकं विश्वं ब्रह्माण्डविवरान्तरम् ॥ १३ ॥
ITRANS:
tata ekodakaṁ viśvaṁbrahmāṇḍa-vivarāntaram
Translation:
At that time, the shell of the universe will fill up with water, forming a single cosmic ocean.