Mark 10:2-12  NAS

Some Pharisees came up to Jesus, testing Him, and began to question Him whether it was lawful for a man to divorce a wife.  And He answered and said to them, "What did Moses command you?"  They said, "Moses permitted a man TO WRITE A CERTIFICATE OF DIVORCE AND SEND her AWAY."  But Jesus said to them, "Because of your hardness of heart he wrote you this commandment.  But from the beginning of creation, God MADE THEM MALE AND FEMALE.  FOR THIS REASON A MAN SHALL LEAVE HIS FATHER AND MOTHER, AND THE TWO SHALL BECOME ONE FLESH; so they are no longer two, but one flesh.  What therefore God has joined together, let no man separate." 
 
In the house the disciples began questioning Him about this again.  And He said to them, "Whoever divorces his wife and marries another woman commits adultery against her; and if she herself divorces her husband and marries another man, she is committing adultery."