Augustine of Hippo
Catena Aurea · Matthäusevangelium 5
It hath been said, Whosoever shall put away his wife, let him give her a writing of divorcement: But I say unto you, That whosoever shall put away his wife, saving for the cause of fornication, causeth her to commit adultery: and whosoever shall marry her that is divorced committeth adultery.
(Retract. i. 19. 6.) Yet I would not have the reader think this disputation of ours sufficient in a matter so arduous; for not every sin is spiritual fornication, nor does God destroy every sinner, for He hears His saints daily crying to Him, Forgive us our debts; but every man who goes a whoring and forsakes Him, him He destroys. Whether this be the fornication for which divorce is allowed is a most knotty question—for it is no question at all that it is allowed for the fornication by earnal sin.