Mattityahu 19:6-8

Orthodox Jewish Bible

⁶ So they are no longer shnayim (two) but basar echad (one flesh). Therefore, whatever Hashem joined together, let no man divide asunder.

⁷ They say to him, Why then did Moshe Rabbenu give the mitzvah to give the get, the sefer keritut, and send her away?

⁸ 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.