tasv avatsit sva-srstasu
tena narayano nama
yad apah purusodbhavah
tasu—in that; avatsit—resided; sva—own; srstasu—in the matter of creation; sahasram—one thousand; parivatsaran—years of His measurement; tena—for that reason; narayanah—the Personality of Godhead named Narayana; nama—name; yat—because; apah—water; purusa-udbhavah—emanated from the Supreme Person.
That Supreme Person is not impersonal and therefore is distinctively a nara, or person. Therefore the transcendental water created from the Supreme Nara is known as nara. And because He lies down on that water, He is known as Narayana.
Link to this page: https://prabhupadabooks.com/sb/2/10/11