Surah Al-Hashr — Ayah 4 (59:4)
ذَٰلِكَ بِأَنَّهُمۡ شَآقُّواْ ٱللَّهَ وَرَسُولَهُۥۖ وَمَن يُشَآقِّ ٱللَّهَ فَإِنَّ ٱللَّهَ شَدِيدُ ٱلۡعِقَابِ ٤
English translation (Saheeh International)
That is because they opposed Allāh and His Messenger. And whoever opposes Allāh - then indeed, Allāh is severe in penalty.
Brief commentary
Whatever happened to them happened because they took Allah and His Messenger as enemies through their disbelief and breaking of the treaties. And whoever takes Allah as his enemy, Allah is severe in punishment, so he will soon suffer His sever punishment.