"That is because they opposed Allah and His Messenger." Qatada said: Al-shiqaq (opposition/dissent) is separation.
﴿ذَلِكَ بِأَنَّهُمْ شَاقُّوا اللَّهَ وَرَسُولَهُ﴾ قَالَ قَتَادَة: الشقاق: الْفِرَاق
