ذٰلِكَ بِأَنَّهُم شاقُّوا اللَّهَ وَرَسولَهُ ۚ وَمَن يُشاقِقِ اللَّهَ وَرَسولَهُ فَإِنَّ اللَّهَ شَديدُ العِقابِ

That is because they opposed Allah and His Messenger. And whoever opposes Allah and His Messenger - indeed, Allah is severe in penalty.