Question Summary:
Wife called me Kafir

Question Detail:

Aswrwb, my wife called me a kaafir... does that break my nikah..???

Answer :

A Kafir is a person who disbelieves in any one of the necessities of Deen. ^[1] Calling someone Kafir does not make the person a Kafir. However, a person must be very cautious in branding someone a Kafir as it has severe consequences. ^[2]
Consider the following Hadith:
Ibn 'Umar (Radhiyallahu Anhu) said:
The Messenger of Allah ﷺ said:
“When a person calls his brother (in Islam) a disbeliever, one of them will certainly deserve the title. If the person whom he addressed was eligible for this, he will return with it. If not, it will go back to the person who made this statement.” [Muslim] ^[3]
 
Taking into consideration the above, you should caution your wife not to utter such words. Nonetheless, your Nikah is intact.
And Allah Ta’āla Knows Best
Safwaan Ibn Ml Ahmed Ibn Ibrahim  
Student Darul Iftaa
Limbe, Malawi
Checked and Approved by,
Mufti Ismail Desai.
___________________________
[1] Fatawa Mahmudiyya; Vol. 2. Pg. 81-2 – Mahmudiyya
[2] Fatawa Mahmudiyya; Vol. 2. Pg. 188-192, 194-5 – Mahmudiyya
صحيح مسلم (1/ 79) - دار إحياء التراث العربي - بيروت [3]
وَحَدَّثَنَا يَحْيَى بْنُ يَحْيَى التَّمِيمِيُّ، وَيَحْيَى بْنُ أَيُّوبَ، وَقُتَيْبَةُ بْنُ سَعِيدٍ، وَعَلِيُّ بْنُ حُجْرٍ جَمِيعًا، عَنْ إِسْمَاعِيلَ بْنِ جَعْفَرٍ، قَالَ يَحْيَى بْنُ يَحْيَى: أَخْبَرَنَا إِسْمَاعِيلُ بْنُ جَعْفَرٍ، عَنْ عَبْدِ اللهِ بْنِ دِينَارٍ أَنَّهُ سَمِعَ ابْنَ عُمَرَ، يَقُولُ: قَالَ رَسُولُ اللهِ صَلَّى اللهُ عَلَيْهِ وَسَلَّمَ: " أَيُّمَا امْرِئٍ قَالَ لِأَخِيهِ: يَا كَافِرُ، فَقَدْ بَاءَ بِهَا أَحَدُهُمَا، إِنْ كَانَ كَمَا قَالَ، وَإِلَّا رَجَعَتْ عَلَيْهِ