In the Bhakti-rasāmṛta-sindhu (2.1.4-5), the following definition is given: athāsyāḥ keśava-rater lakṣitāyā nigadyatesāmagrī-paripoṣeṇa paramā rasa-rūpatā vibhāvair anubhāvaiś ca sāttvikair vyabhicāribhiḥsvādyatvaṁ hṛdi bhaktānām ānītā śravaṇādibhiḥeṣā kṛṣṇa-ratiḥ sthāyī bhāvo bhakti-raso bhavet “Love for Kṛṣṇa, Keśava, as previously described, reaches the supreme state of being composed of mellows when its ingredients are fulfilled. By means of vibhāva, anubhāva, sāttvika and vyabhicārī, hearing and chanting are activated, and the devotee is able to taste love for Kṛṣṇa. Then attachment for Kṛṣṇa, or permanent ecstasy (sthāyi-bhāva), becomes the mellow of devotional service (bhakti-rasa).”