This is a verse from the Bhakti-rasāmṛta-sindhu (1.2.59). Here Śrīla Kṛṣṇadāsa Kavirāja says that Lord Caitanya spoke the verse to Veṅkata Bhaṭṭa, and earlier he said that Veṅkata Bhaṭṭa spoke it to the Lord. But since their conversation took place long, long before the Bhakti-rasāmṛta-sindhu was composed, the question my be raised as to how either of them quoted the verse. Śrīla Bhaktivinoda Ṭhākura explains that this verse and many others like it were current among devotees long before the Bhakti-rasāmṛta-sindhu was composed. Thus devotees would always quote them and explain their purport in ecstasy.