Ibn Taymiyyah on Excommunication: It is forbidden to declare a Muslim to be a disbeliever on account of his sins

Ibn Taymiyyah, may Allah have mercy on him, said, “It is not permissible to excommunicate a Muslim because of his sinful deeds… The Kharijite sect was the first to declare Muslims to be unbelievers because of their sins, and they declared as unbelievers whoever differed with them in their innovations, and they made lawful the spilling of blood and the taking of wealth. This is the condition of the people of innovation, that they invent some religious innovation and then they excommunicate whoever disagrees with them concerning it. Rather, the people of the Sunnah and the community follow the Book and the Sunnah and they obey Allah and His Messenger and follow the truth. They have mercy upon the creation.”

Source: Majmū’ al-Fatāwá 1/278

قال شيخ ابن تيمية لا يجوز تكفير المسلم بذنب فعله … وَالْخَوَارِجُ هُمْ أَوَّلُ مَنْ كَفَّرَ الْمُسْلِمِينَ يُكَفِّرُونَ بِالذُّنُوبِ ، وَيُكَفِّرُونَ مَنْ خَالَفَهُمْ فِي بِدْعَتِهِمْ وَيَسْتَحِلُّونَ دَمَهُ وَمَالَهُ وَهَذِهِ حَالُ أَهْلِ الْبِدَعِ يَبْتَدِعُونَ بِدْعَةً وَيُكَفِّرُونَ مَنْ خَالَفَهُمْ فِيهَا وَأَهْلُ السُّنَّةِ وَالْجَمَاعَةِ يَتَّبِعُونَ الْكِتَابَ وَالسُّنَّةَ وَيُطِيعُونَ اللَّهَ وَرَسُولَهُ فَيَتَّبِعُونَ الْحَقَّ وَيَرْحَمُونَ الْخَلْقَ

1/278 مجموع فتاوى ابن تيمية العقيدة كتاب مجمل اعتقاد السلف قاعدة أهل السنة والجماعة الاعتصام بالكتاب والسنة وعدم الفرقة فصل لا يجوز تكفير المسلم بذنب فعله