SB 4.1.59
tav imau vai bhagavato
harer amsav ihagatau
bhara-vyayaya ca bhuvah
krsnau yadu-kurudvahau
Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
That Nara-Narayana Rsi, who is a partial expansion of Krsna, has now appeared in the dynasties of Yadu and Kuru, in the forms of Krsna and Arjuna respectively, to mitigate the burden of the world.
Purport by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
Narayana is the Supreme Personality of Godhead, and Nara is a part of the Supreme Personality of Godhead, Narayana. Thus the energy and the energetic together are the Supreme Personality of Godhead. Maitreya informed Vidura that Nara, the portion of Narayana, had appeared in the family of the Kurus and that Narayana, the plenary expansion of Krsna, had come as Krsna, the Supreme Personality of Godhead, with the purpose of delivering suffering humanity from the pangs of material burdens. In other words, Narayana Rsi was now present in the world in the forms of Krsna and Arjuna.