Mark 10:6-12: [Christ said,] "From the beginning of creation, 'God made them male and female. Therefore a man shall leave his father and 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." And in the house the disciples asked him again about this matter. 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."
Hebrews 13:4: Let marriage be held in honor among all, and let the marriage bed be undefiled, for God will judge the sexually immoral and adulterous.