CC Ādi 5.132

yei yei rūpe jāne, sei tāhā kahe
sakala sambhave kṛṣṇe, kichu mithyā nahe
Word for word: 
yei yei — whatever; rūpe — in the form; jāne — one knows; sei — he; tāhā — that; kahe — says; sakala sambhave kṛṣṇe — everything is possible in Kṛṣṇa; kichu mithyā nahe — there is no falsity.
Translation: 
In whatever form one knows the Lord, one speaks of Him in that way. In this there is no falsity, since everything is possible in Kṛṣṇa.
Purport: 

In this connection we may mention an incident that took place between two of our sannyāsīs while we were preaching the Hare Kṛṣṇa mahā-mantra in Hyderabad. One of them stated that “Hare Rāma” refers to Śrī Balarāma, and the other protested that “Hare Rāma” means Lord Rāma. Ultimately the controversy came to me, and I gave the decision that if someone says that the “Rāma” in “Hare Rāma” is Lord Rāmacandra and someone else says that the “Rāma” in “Hare Rāma” is Śrī Balarāma, both are correct because there is no difference between Śrī Balarāma and Lord Rāma. Here in Śrī Caitanya-caritāmṛta we find that Kṛṣṇadāsa Kavirāja Gosvāmī has stated the same conclusion:

yei yei rūpe jāne, sei tāhā kahe
sakala sambhave kṛṣṇe, kichu mithyā nahe

If someone calls Lord Rāmacandra by the vibration Hare Rāma, understanding it to mean “O Lord Rāmacandra!” he is quite right. Similarly, if one says that Hare Rāma means “O Śrī Balarāma!” he is also right. Those who are aware of the viṣṇu-tattva do not fight over all these details.

In the Laghu-bhāgavatāmṛta Śrīla Rūpa Gosvāmī has explained Kṛṣṇa’s being both Kṣīrodakaśāyī Viṣṇu and Nārāyaṇa in the spiritual sky and expanding in the quadruple forms known as Vāsudeva, Saṅkarṣaṇa, Pradyumna and Aniruddha. He has refuted the idea that Kṛṣṇa is an incarnation of Nārāyaṇa. Some devotees think that Nārāyaṇa is the original Personality of Godhead and that Kṛṣṇa is an incarnation. Even Śaṅkarācārya, in his commentary on the Bhagavad-gītā, has accepted Nārāyaṇa as the transcendental Personality of Godhead who appeared as Kṛṣṇa, the son of Devakī and Vasudeva. Therefore this matter may be difficult to understand. But the Gauḍīya Vaiṣṇava-sampradāya, headed by Rūpa Gosvāmī, has established the principle of the Bhagavad-gītā that everything emanates from Kṛṣṇa, who says in the Bhagavad-gītā, ahaṁ sarvasya prabhavaḥ: “I am the original source of everything.” “Everything” includes Nārāyaṇa. Therefore Rūpa Gosvāmī, in his Laghu-bhāgavatāmṛta, has established that Kṛṣṇa, not Nārāyaṇa, is the original Personality of Godhead.

In this connection he has quoted a verse from Śrīmad-Bhāgavatam (3.2.15) that states:

sva-śānta-rūpeṣv itaraiḥ svarūpair
abhyardyamāneṣv anukampitātmā
parāvareśo mahad-aṁśa-yukto
hy ajo ’pi jāto bhagavān yathāgniḥ

“When pure devotees of the Lord like Vasudeva are greatly disturbed by dangerous demons like Kaṁsa, Lord Kṛṣṇa joins with all His pastime expansions, such as the Lord of Vaikuṇṭha, and, although unborn, becomes manifest, just as fire becomes manifest by the friction of araṇi wood.” Araṇi wood is used to ignite a sacrificial fire without matches or any other flame. Just as fire appears from araṇi wood, the Supreme Lord appears when there is friction between devotees and nondevotees. When Kṛṣṇa appears, He appears in full, including within Himself all His expansions, such as Nārāyaṇa, Vāsudeva, Saṅkarṣaṇa, Aniruddha and Pradyumna. Kṛṣṇa is always integrated with His other incarnations, like Nṛsiṁhadeva, Varāha, Vāmana, Nara-Nārāyaṇa, Hayagrīva and Ajita. In Vṛndāvana Lord Kṛṣṇa sometimes exhibits the functions of such incarnations.

In the Brahmāṇḍa Purāṇa it is said, “The same Personality of Godhead who is known in Vaikuṇṭha as the four-handed Nārāyaṇa, the friend of all living entities, and in the milk ocean as the Lord of Śvetadvīpa, and who is the best of all puruṣas, appeared as the son of Nanda. In a fire there are many sparks of different dimensions; some of them are very big, and some are small. The small sparks are compared to the living entities, and the large sparks are compared to the Viṣṇu expansions of Lord Kṛṣṇa. All the incarnations emanate from Kṛṣṇa, and after the end of their pastimes they again merge with Kṛṣṇa.”

Therefore in the various Purāṇas Kṛṣṇa is described sometimes as Nārāyaṇa, sometimes as Kṣīrodakaśāyī Viṣṇu, sometimes as Garbhodakaśāyī Viṣṇu and sometimes as Vaikuṇṭhanātha, the Lord of Vaikuṇṭha. Because Kṛṣṇa is always full, Mūla-saṅkarṣaṇa is in Kṛṣṇa, and since all incarnations are manifested from Mūla-saṅkarṣaṇa, it should be understood that He can manifest different incarnations by His supreme will, even in the presence of Kṛṣṇa. Great sages have therefore glorified the Lord by different names. Thus when the original person, the source of all incarnations, is sometimes described as an incarnation, there is no discrepancy.