Bhagavatapurana 2.10.11

2.10.11

tāsvavātsīt svasṛṣṭāsu sahasraṃ parivatsarān /
tena nārāyaṇo nāma yadāpaḥ puruṣodbhavāḥ //

11. On those waters thus created by Himself He dwelt for a thousand long years; for this reason He became known as Narayana, for the waters are produced from Purusha or Nara; (thus waters are *naras*, and *naras* being the *ayana* or resort, He is called Narayana).