Devibhagavatapurana 4.1.15

4.1.15

tayoraṃśāvatārau hi jiṣṇukṛṣṇau mahābalau |
prasiddhau munibhiḥ proktau sarvajñairnāradādibhiḥ ||

The all-knowing sages Nârada and others say that the well known Arjuna and S’rî Krisna of indomitable prowess were the two part incarnations of those two ancient Munis Nara and Nârâyana.