CC Ādi 5.91

sei ta’ puruṣa yāṅra ‘aṁśa’ dhare nāma
caitanyera saṅge sei nityānanda-rāma
Word for word: 
sei ta’ — that; puruṣa — Supreme Person; yāṅra — of whom; aṁśa — as part; dhare nāma — is known; caitanyera saṅge — with Śrī Caitanya Mahāprabhu; sei — that; nityānanda-rāma — Lord Nityānanda or Balarāma.
Translation: 
That Mahā-puruṣa [Kāraṇodakaśāyī Viṣṇu] is known as a plenary part of Him who is Lord Nityānanda Balarāma, the favorite associate of Lord Caitanya.