CC Madhya-lila 21.088 - Padma Purana
Sri Caitanya-caritamrta
CC Madhya-lila
CC Madhya 21.88, Translation and Purport:
“‘“Beyond the river Virajā is the spiritual nature, which is indestructible, eternal, inexhaustible and unlimited. It is the supreme abode, consisting of three fourths of the Lord's opulences. It is known as paravyoma, the spiritual sky.”’
This is a verse from the Padma Purāṇa, quoted here by Lord Kṛṣṇa.