St Mark 10:2-9

And the Pharisees coming to him asked him: Is it lawful for a man to put away his wife? tempting him. But he answering, saith to them: What did Moses command you? Who said: Moses permitted to write a bill of divorce, and to put her away. To whom Jesus answering, said: Because of the hardness of your heart he wrote you that precept. But from the beginning of the creation, God made them male and female. For this cause a man shall leave his father and mother; and shall cleave to his wife. And they two shall be in one flesh. Therefore now they are not two, but one flesh. What therefore God hath joined together, let not man put asunder.