CC Ādi 5.6

sei kṛṣṇa — navadvīpe śrī-caitanya-candra
sei balarāma — saṅge śrī-nityānanda
Word for word: 
sei kṛṣṇa — that original Kṛṣṇa; navadvīpe — at Navadvīpa; śrī-caitanya-candra — Lord Śrī Caitanya Mahāprabhu; sei balarāma — that Lord Balarāma; saṅge — with Him; śrī-nityānanda — Lord Nityānanda.
Translation: 
That original Lord Kṛṣṇa appeared in Navadvīpa as Lord Caitanya, and Balarāma appeared with Him as Lord Nityānanda.