That Nara-Nārāyaṇa Ṛṣi, who is a partial expansion of Kṛṣṇa, has now appeared in the dynasties of Yadu and Kuru, in the forms of Kṛṣṇa and Arjuna respectively, to mitigate the burden of the world.
Srimad Bhagavata Purana
श्रीमद्भागवतमहापुराणम्
मूल श्लोकः
ताविमौ वै भगवतो हरेरंशाविहागतौ । भारव्ययाय च भुवः कृष्णौ यदुकुरूद्वहौ
tāvimau vai bhagavato hareraṃśāvihāgatau | bhāravyayāya ca bhuvaḥ kṛṣṇau yadukurūdvahau
SB 4.1.59