But Nicodemus being unable to take in so great and deep mysteries, our Lord helps him by the analogy of our carnal birth, saying, That which is born of the flesh is flesh, and that which is born of the Spirit is spirit. For as flesh generates flesh, so also doth spirit spirit.
Reproduced in full. Translation: Oxford 1841 (Newman), public domain (Public domain).
Also cites: Hom. in Oct. Pent.