CC Madhya 25.78
jīve ‘viṣṇu’ māni — ei aparādha-cihna
prabhu kahe — Lord Śrī Caitanya Mahāprabhu said; viṣṇu viṣṇu — the holy name of Viṣṇu; āmi — I; kṣudra — infinitesimal; jīva — a living entity; hīna — bereft of all good qualities; jīve — such a low-grade living entity; viṣṇu māni — accepting as Lord Viṣṇu or the Personality of Godhead; ei aparādha-cihna — this is a great offense.
When Prakāśānanda Sarasvatī supported himself by quoting the verse from Śrīmad-Bhāgavatam, Śrī Caitanya Mahāprabhu immediately protested by uttering the holy name of Lord Viṣṇu. The Lord then presented Himself as a most fallen living entity, and He said, “If someone accepts a fallen conditioned soul as Viṣṇu, Bhagavān, or an incarnation, he commits a great offense.”
Although Śrī Caitanya Mahāprabhu was Viṣṇu, the Supreme Personality of Godhead, to teach us a lesson He nonetheless denied belonging to the Viṣṇu category. Unfortunately, there are many so-called Viṣṇu incarnations in this Age of Kali. People do not know that posing oneself as an incarnation is most offensive. People should not accept an ordinary man as an incarnation of God, for this also is a very great offense.