Is it permissible for a Sunni man to marry a woman who differs with him in madhhab, with her father stipulating that he not try to convince her of the madhhab of Ahl al-Sunnah wal-Jama'ah, and would the marriage become invalid if the husband later violates this condition?

The Bid'ah (innovation) of the people of innovation is divided into two categories: that which constitutes disbelief (mukaffirah), in which case marriage to a woman who holds such innovation is not permissible; and that which does not constitute disbelief (ghayr mukaffirah), in which case marriage to her is permissible. However, it is preferable not to marry an innovator at all, due to the absence of the quality of religiosity in her. If one wishes to marry her, it is not permissible for him to submit to a condition that prevents him from teaching her and raising her upon goodness, as the husband is enjoined by sacred law to do so, based on the Almighty's saying: ﴿O YOU WHO HAVE BELIEVED, PROTECT YOURSELVES AND YOUR FAMILIES FROM A FIRE﴾ (Quran 66:6). If he agrees to the condition and then violates it, this does not affect the validity of the marriage.