Matthew 19:4-6

He replied, Have you never read that He Who made them from the beginning made them male and female, And said, For this reason a man shall leave his father and mother and shall be united firmly (joined inseparably) to his wife, and the two shall become one flesh? [Gen. 1:27; 2:24.] So they are no longer two, but one flesh. What therefore God has joined together, let not man put asunder (separate).