Matthew 19:7-9

7They say unto him, Why did Moses then command to give a writing of divorcement, and to put her away?

8He saith unto them, Moses because of the hardness of your hearts suffered you to put away your wives: but from the beginning it was not so.

9And I say unto you, Whosoever shall put away his wife, except it be for fornication, and shall marry another, committeth adultery: and whoso marrieth her which is put away doth commit adultery.