Matthew 19:6

3 The Pharisees also came unto him, tempting him, and saying unto him, Is it lawful for a man to put away his wife for every cause?

4 And he answered and said unto them, Have ye not read, that he which made them at the beginning made them male and female,

5 And said, For this cause shall a man leave father and mother, and shall cleave to his wife: and they twain shall be one flesh?

6 Wherefore they are no more twain, but one flesh. What therefore God hath joined together, let not man put asunder.

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

8 He 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.

9 And 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.