Matthew 19:5-8

and said, ‘Therefore a man shall leave his father and his mother and hold fast to his wife, and the two shall become one flesh’? So they are no longer two but one flesh. What therefore God has joined together, let not man separate.” They said to him, “Why then did Moses command one to give a certificate of divorce and to send her away?” He said to them, “Because of your hardness of heart Moses allowed you to divorce your wives, but from the beginning it was not so.