Matthew 19:3-9

And the Pharisees came to him tempting him, and saying, Is it lawful for a man to put away his wife for every cause? But he answering said to them, Have ye not read that he who made them, from the beginning made them male and female, and said, On account of this a man shall leave father and mother, and shall be united to his wife, and the two shall be one flesh? so that they are no longer two, but one flesh. What therefore God has joined together, let not man separate. They say to him, Why then did Moses command to give a letter of divorce and to send her away? He says to them, Moses, in view of your hardheartedness, allowed you to put away your wives; but from the beginning it was not thus. But I say unto you, that whosoever shall put away his wife, not for fornication, and shall marry another, commits adultery; and he who marries one put away commits adultery.