• أَنكَٰث
• نَّكَثَ
• نَّكَثُوٓا۟
• يَنكُثُ
• يَنكُثُونَ

Appears 6 times in the Quran.

1. 7:135 فَلَمَّا كَشَفْنَا عَنْهُمُ ٱلرِّجْزَ إِلَىٰٓ أَجَلٍ هُم بَٰلِغُوهُ إِذَا هُمْ يَنكُثُونَ

   But when We removed the plague from them till a term which they should attain lo! they broke (the promise).
   

2. 9:12 وَإِن نَّكَثُوٓا۟ أَيْمَٰنَهُم مِّنۢ بَعْدِ عَهْدِهِمْ وَطَعَنُوا۟ فِى دِينِكُمْ فَقَٰتِلُوٓا۟ أَئِمَّةَ ٱلْكُفْرِ إِنَّهُمْ لَآ أَيْمَٰنَ لَهُمْ لَعَلَّهُمْ يَنتَهُونَ

   And if they break their oaths after their agreement and (openly) revile your religion, then fight the leaders of unbelief-- surely their oaths are nothing-- so that they may desist.
   

3. 9:13 أَلَا تُقَٰتِلُونَ قَوْمًا نَّكَثُوٓا۟ أَيْمَٰنَهُمْ وَهَمُّوا۟ بِإِخْرَاجِ ٱلرَّسُولِ وَهُم بَدَءُوكُمْ أَوَّلَ مَرَّةٍ أَتَخْشَوْنَهُمْ فَٱللَّهُ أَحَقُّ أَن تَخْشَوْهُ إِن كُنتُم مُّؤْمِنِينَ

   What! will you not fight a people who broke their oaths and aimed at the expulsion of the Messenger, and they attacked you first; do you fear them? But Allah is most deserving that you should fear Him, if you are believers.
   

4. 16:92 وَلَا تَكُونُوا۟ كَٱلَّتِى نَقَضَتْ غَزْلَهَا مِنۢ بَعْدِ قُوَّةٍ أَنكَٰثًا تَتَّخِذُونَ أَيْمَٰنَكُمْ دَخَلًۢا بَيْنَكُمْ أَن تَكُونَ أُمَّةٌ هِىَ أَرْبَىٰ مِنْ أُمَّةٍ إِنَّمَا يَبْلُوكُمُ ٱللَّهُ بِهِۦ وَلَيُبَيِّنَنَّ لَكُمْ يَوْمَ ٱلْقِيَٰمَةِ مَا كُنتُمْ فِيهِ تَخْتَلِفُونَ

   And be not like her who unravels her yarn, disintegrating it into pieces after she has spun it strongly. You make your oaths to be means of deceit between you because (one) nation is more numerous than (another) nation. Allah only tries you by this; and He will most certainly make clear to you on the resurrection day that about which you differed.
   

5. 43:50 فَلَمَّا كَشَفْنَا عَنْهُمُ ٱلْعَذَابَ إِذَا هُمْ يَنكُثُونَ

   But when We removed from them the chastisement, lo! they broke the pledge.
   

6. 48:10 إِنَّ ٱلَّذِينَ يُبَايِعُونَكَ إِنَّمَا يُبَايِعُونَ ٱللَّهَ يَدُ ٱللَّهِ فَوْقَ أَيْدِيهِمْ فَمَن نَّكَثَ فَإِنَّمَا يَنكُثُ عَلَىٰ نَفْسِهِۦ وَمَنْ أَوْفَىٰ بِمَا عَٰهَدَ عَلَيْهُ ٱللَّهَ فَسَيُؤْتِيهِ أَجْرًا عَظِيمًا

   Surely those who swear allegiance to you do but swear allegiance to Allah; the hand of Allah is above their hands. Therefore whoever breaks (his faith), he breaks it only to the injury of his own soul, and whoever fulfills what he has covenanted with Allah, He will grant him a mighty reward.