This question already has an answer here:
And now, let us make a covenant with our God to cast out all the wives and their offspring, by the counsel of the lord and those who hasten to [perform] the commandment of our God, and according to the Law it shall be done.
וְעַתָּה נִכְרָת בְּרִית לֵאלֹהֵינוּ לְהוֹצִיא כָל נָשִׁים וְהַנּוֹלָד מֵהֶם בַּעֲצַת אֲדֹנָי וְהַחֲרֵדִים בְּמִצְוַת אֱלֹהֵינוּ וְכַתּוֹרָה יֵעָשֶׂה׃
and according to the Law it shall be done: he who performs this act, who will cast out his gentile wife and children.
I'm not clear if this means that the law says this is what is to be done, or if it means that is shall be done in the way the law says to do it?
Either way, does anyone know where the law addresses this?