Dought & clear, - The difference between a Jewish or Christian wife and a wife who does not pray.

I read a fatwa which you issued to a Muslim man whose Muslim wife does
not pray, and you told him that he had to divorce her. I know that it
is permissible for a Muslim man to have a Jewish or Christian wife,
and Jewish and Christian women do not pray. Is there some mistake?.
Praise be to Allaah.
There is no mistake in the fatwa referred to. Rather the mistake comes
from the questioner wanting to regard as equal a woman who is
supposedly Muslim but does not pray and a woman who is Jewish or
Christian, on the basis that neither of them prays.
This regarding them as equal is not valid, because there is a
difference between them, which is that not praying is major kufr and
apostasy that puts a person beyond the pale of Islam. This has been
explained in many answers on this site, such as the answers to
questions no. 9400and 5208.
Based on this, the woman who does not pray is a kaafir and an apostate
from Islam.
The ruling on one who has apostatized from Islam is more severe than
the ruling on a Jew or Christian.
Shaykh al-Islam Ibn Taymiyah said:
The apostate is worse than a kaafir in many ways. End quote.
Majmoo' al-Fataawa, 2/193
Hence meat slaughtered by an apostate cannot be eaten, whereas meat
slaughtered by a Jew or Christian may be eaten. It is not permissible
for a Muslim to marry an apostate woman, and if his wife apostatizes,
the marriage contract becomes null and void, but it is permissible for
a Muslim to marry a Jewish or Christian woman.
The crux of the matter is the ruling that one who does not pray is a
kaafir. Those who are of this view forbade marriage to a woman who
does not pray, and said that it is obligatory to leave a woman if she
stops praying. This is the view of Imam Ahmad (may Allaah have mercy
on him) and was stated in fatwas by a number of scholars, such as
Shaykh Ibn Baaz (may Allaah have mercy on him), Shaykh Ibn 'Uthaymeen
(may Allaah have mercy on him) and Shaykh Saalih al-Fawzaan (may
Allaah preserve him). Our fatwa on this issue and similar issues is
based on their fatwas.
Similarly, if a woman does something that implies kufr, such as
vilifying Allaah, may He be exalted, or vilifying His Messenger(peace
and blessings of Allaah be upon him), and she persists in her kufr and
does not repent, then it is not permissible for her to remain the wife
of a Muslim. The same applies if a husband is ruled to be an apostate,
then he and his wife must be separated.
And Allaah knows best.