Mattityahu 19:3-9

And the Perushim approached him with a she'elah to test him, and they asked him, Is it mutar (permissible) for a man to give a get (divorce) to his wife for any and every reason? But Rebbe, Melech HaMoshiach said in reply, Have you not read that HaBoreh (The Creator, Yotzer) bereshis (in the beginning) created them zachar (male) and nekevah (female)? And he said, Because of this, YAAZAV ISH ES AVIV VES IMMO VDAVAK BISHTO VHAYU LVASAR ECHAD (a man will leave his father and his mother and will be joined to his isha (wife), and the two will be one flesh). So they are no longer shnayim (two) but basar echad (one flesh). Therefore, whatever HASHEM joined together, let no man divide asunder. They say to him, Why then did Moshe Rabbenu give the mitzvah to give the get, the sefer keritut, and send her away? He says to them, Moshe, because of your hardness of heart, permitted you to give the get to your wives; but from bereshis (in the beginning), however, it was not so. But I say to you that whoever, the case of zenut (fornication) being excepted, gives the get to his wife and marries another, is guilty of niuf (adultery).