Origen

Perhaps some one will say, that Jesus in thus speaking, suffered wives to be put away for the same cause that Moses suffered them, which He says was for the hardness of the hearts of the Jews. But to this it is to be answered, that if by the Law an adulteress is stoned, that sin is not to be understood as the shameful thing for which Moses suffers a writing of divorcement; (Deut. 24:1.) for in a cause of adultery it was not lawful to give a writing of divorcement. But Moses perhaps calls every sin in a woman a shameful thing, which if it be found in her, a bill of divorcement is written against her. But we should enquire, If it is lawful to put away a wife for the cause of fornication only, what is it if a woman be not an adulteress, but have done any other heinous crime; have been found a poisoner, or to have murdered her children? The Lord has explained this matter in another place, saying, Whoso putteth her away, except for the cause of fornication, maketh her to commit adultery, (Mat. 5:32.) giving her an opportunity of a second marriage.