CC Ādi 3.72

advaita, nityānanda — caitanyera dui aṅga
aṅgera avayava-gaṇa kahiye upāṅga
Synonyms: 
advaita — Advaita Ācārya; nityānanda — Lord Nityānanda; caitanyera — of Lord Caitanya Mahāprabhu; dui — two; aṅga — limbs; aṅgera — of the limbs; avayava-gaṇa — the constituent parts; kahiye — I say; upāṅga — parts.
Translation: 
Śrī Advaita Prabhu and Śrī Nityānanda Prabhu are both plenary portions of Lord Caitanya. Thus They are the limbs [aṅgas] of His body. The parts of these two limbs are called the upāṅgas.