CC Madhya 9.117
rūpam eṣā rasa-sthitiḥ
siddhāntataḥ — in reality; tu — but; abhede — no difference; api — although; śrī-īśa — of the husband of Lakṣmī, Nārāyaṇa; kṛṣṇa — of Lord Kṛṣṇa; svarūpayoḥ — between the forms; rasena — by transcendental mellows; utkṛṣyate — is superior; kṛṣṇa-rūpam — the form of Lord Kṛṣṇa; eṣā — this; rasa-sthitiḥ — reservoir of pleasure.
Veṅkaṭa Bhaṭṭa continued, “ ‘According to transcendental realization, there is no difference between the forms of Nārāyaṇa and Kṛṣṇa. Yet in Kṛṣṇa there is a special transcendental attraction due to the conjugal mellow, and consequently He surpasses Nārāyaṇa. This is the conclusion of transcendental mellows.’
This verse quoted by Veṅkaṭa Bhaṭṭa is also found in the Bhakti-rasāmṛta-sindhu (1.2.59).