CC Ādi 1.37

ei chaya guru — śikṣā-guru ye āmāra
tāṅ’-sabāra pāda-padme koṭi namaskāra
Synonyms: 
ei — these; chaya — six; guru — spiritual masters; śikṣā-guru — instructing spiritual masters; ye — who are; āmāra — my; tāṅ’-sabāra — of all of them; pāda-padme — unto the lotus feet; koṭi — ten million; namaskāra — respectful obeisances.
Translation: 
These six are my instructing spiritual masters, and therefore I offer millions of respectful obeisances unto their lotus feet.
Purport: 

By accepting the six Gosvāmīs as his instructing spiritual masters, the author specifically makes it clear that one should not be recognized as a Gauḍīya Vaiṣṇava if he is not obedient to them.