And from there he set out [and] came to the region of Judea and the other side of the Jordan, and again crowds came together to him. And again, as he was accustomed [to do], he began to teach them.
And they asked him if it was permitted for a man to divorce [his] wife, [in order to] test him.
And he answered [and] said to them, "What did Moses command you?"
So they said, "Moses permitted [a man] to write a certificate of divorce and to send [her] away."
But Jesus said to them, "He wrote this commandment for you because of your hardness of heart.
But from the beginning of creation 'he made them male and female.
Because of this a man will leave his father and mother and will be joined to his wife,
and the two will become one flesh,' so that they are no longer two but one flesh.
Therefore what God has joined together, man must not separate."
And in the house again the disciples began to ask him about this.
References for Mark 10:10
And he said to them, "Whoever divorces his wife and marries another commits adultery against her.
And if she divorces her husband [and] marries another, she commits adultery."
References for Mark 10:12