وَجَائِزٌ أَنْ يُنْسَخَ التَّطَوُّعُ ثَانِيًا فَيُفْرَضَ الْفَرْضُ الْأَوَّلُ كَمَا كَانَ فِي الِابْتِدَاءِ فَرْضًا
And it is also permissible that a voluntary act (nafl) be abrogated and made obligatory again, just as in the beginning it was obligatory.