CC Ādi 2.61

avatārī nārāyaṇa, kṛṣṇa avatāra
teṅha catur-bhuja, iṅha manuṣya-ākāra
Word for word: 
avatārī — source of incarnations; nārāyaṇa — Lord Nārāyaṇa; kṛṣṇa — Lord Kṛṣṇa; avatāra — incarnation; teṅha — that; catuḥ-bhuja — four arms; iṅha — this; manuṣya — like a man; ākāra — form.
Translation: 
Because Nārāyaṇa has four hands whereas Kṛṣṇa looks just like a man, they say that Nārāyaṇa is the original God whereas Kṛṣṇa is but an incarnation.
Purport: 

Some scholars argue that because Nārāyaṇa has four hands whereas Śrī Kṛṣṇa has only two, Nārāyaṇa is the original Personality of Godhead and Kṛṣṇa is His incarnation. Such unintelligent scholars do not understand the features of the Absolute.