Mark 10:1-11 NIV
Jesus then left that place and went into the region of Judea and across the Jordan. Again crowds of people came to him, and as was his custom, he taught them.
Some Pharisees came and tested him by asking, “Is it lawful for a man to divorce his wife?”
“What did Moses command you?” he replied.
They said, “Moses permitted a man to write a certificate of divorce and send her away.”
“It was because your hearts were hard that Moses wrote you this law,” Jesus replied. “But at the beginning of creation God ‘made them male and female.’ ‘For this reason a man will leave his father and mother and be united to his wife, and the two will become one flesh.’ So they are no longer two, but one flesh. Therefore what God has joined together, let no one separate.”
When they were in the house again, the disciples asked Jesus about this. He answered, “Anyone who divorces his wife and marries another woman commits adultery against her.
NIV: New International Version